Use the info here with consideration. It might be outdated or biased info.
Level Transfusion to level 5, as it is Vladimir's most constant single target damage ability, as well as his heal. Remember that the base healing component is a flat amount modified by additional ability power, so even if the target is not damaged (i.e. shielded, blocked by Banshee's Veil, or blocked by Kayle'sIntervention), you will still be healed by the ability.
Having at least 1 rank of Sanguine Pool can help you survive for much longer, as it resets aggro. A skilled player can use it to turret dive or to dodge abilities. However, it has a long cooldown and a short duration, so do not become too reliant on it for escapes.
It is wise to use Sanguine Pool to chase down an enemy or escaping from one, as there is a slight movespeed burst when Vladimir becomes the pool. Using it as a damage skill could leave you extremely vulnerable if you can't kill the enemy.
While in Sanguine Pool Vladimir is not affected by any auras, including auras from items. While no ally or enemy aura will affect him, Vladimir can still take damage from DoT spells like Fiddlesticks'sDrain and Swain'sTorment, and due to the heavy cost of Sanguine Pool, using it to "escape" such spells can actually harm badly.
Tides of Blood can be cast without having any enemy targets nearby. This can allow you to keep the buff constantly active or build stacks to prepare for an attack. It can also increase the effectiveness of a Health Potion if used prior to activating it. Additionally, using it when a stealthed enemy is nearby will allow you to detect them, they will not destealth, but you will be able to see the missiles flying into their direction. This also works if an enemy is concealed in brush nearby.
Gaining stacks of Tides of Blood prior to a gank can result in devastatingly high nuking ability upon multiple enemies. For the same reason, Vladimir's damage output rises dramatically after about 10 seconds during team fights as his stacks increase very quickly, which can result in massive AoE damage when combined with Hemoplague.
Hemoplague causes targets to take bonus damage, so it is advised to use it at the beginning of team fights to increase the overall damage your team can inflict upon your enemies. Mid to late game, Banshee's Veil will negate both the increased damage debuff and the 5 second delayed damage component, make sure to spend as many of the opposing team's charges prior to activating.
You don't necessarily have to combine it with AoE ultimates. Hemoplague also works well with any champion that packs a lot of AoE damage, such as Malzahar, Brand, Karthus and Riven.
Hemoplague can be used to finish off a target low on health. The range to the edge of the AoE is deceptively long; keep this in mind when deciding whether to pursue a target near death.
When using Hemoplague, be wary of champions who can counter the delayed damage, such as those with shields or heals. Do not depend on it to ensure your kill.
Casting Hemoplague will not deal any immediate damage, and therefore can be used to kill low health enemies under their turret, unless they can heal (e.g. Nidalee) or shield (e.g. Orianna) themselves before the damage takes place.
Spellvamp will heal as soon as spell damage is inflicted on a target, so his Transfusion will have a two part heal, one on damage and one as the particle effects reach him. This healing goes for all of his spells as they deal damage. An unexpected heal may occur when his ultimate Hemoplague pops its damage. However, the heal will be smaller as AoE spells heal for a percentage less than normal.
Vladimir's Passive, Crimson Pact, allows him to be deceptively tanky while dealing high damage. By building large amounts of AP, Vladimir can bypass Health and focus on damage and durability.
With about 320 AP, Transfusion alone can cover the cost of Tides of Blood with max stacks, without having to buy any spellvamp items (100 AP is needed to cover the cost of Tides of Blood without any stack). This allows Vladimir to potentially forgo Hextech Revolver in favor of items that offer other better stats, such as Haunting Guise. Keep in mind, however, that spellvamp will allow Vladimir to cover that cost much better early game, as well as allowing him to have a higher net health gain late-game. Thus, purchasing a Hextech Revolver is still heavily recommended.
Another item that is almost a core for Vladimir is Zhonya's Hourglass, as it provides 168 bonus HP along with the 100 AP and 50 armor. This item allows Vladimir to save his Sanguine Pool to escape on other situations. It also gives Vladimir a much better teamfighting potential.
In terms of start items, Doran's Shield is the best starting item. This gives Vladimir health, and as such, an amount of AP, a very small one however. But even better, this item provides health regeneration, which may be able to mitigate Vladimir's health costs to some extent during early game. It is a very good start against champions who auto-attack from a distance or have single-target spells that harass a lot, such as Ryze. Keep in mind that starting with a Doran's Shield will only allow you to start with a single health potion.
Cloth Armor + 5 potions is a better against AD casters such as Pantheon or Riven, as they don't auto-attack frequently and the armor helps more against them. Also, they harass so constantly that the 5 potions will outheal Doran's Shield health regeneration during early game.
Don't start with Doran's Ring. Although this item offers both AP and health, this item's mana regeneration passive is completely useless for Vladimir (or any manaless champion for that matter), and it doesn't provide health regeneration, unlike Doran's Shield.
Starting with a Amplifying Tome + 1 potion allows Vladimir to deal more damage during early game and to purchase a Hextech Revolver much earlier, but this is a very risky starting item, as Vladimir's early game is very weak, and not having the health regeneration of Doran's Shield or the armor from Cloth Armor will make him have a much harder time in lane. Vladimir doesn't need the extra damage early game as he is a late game champion. Only start with Amplifying Tome if you are sure that you will win your lane early (very hard to happen).
Void Staff is needed if you wish to do significant damage late game.
Other good boots of choice are Ninja Tabi and Mercury's Treads if Vladimir is losing the lane or building tanky. The latter is also good if Vladimir is being focused by enemies crowd control.
Rabadon's Deathcap is one of the most popular items on Mages. However, because of Vladimir'sCrimson Pact, it also grants 210 health and the 30% bonus AP gained interacts with his passive, making it even more cost effective and powerful.
If you want to focus only on Vladimir's damage, though, it is better to leave Rabadon's Deathcap for late game, and buy magic penetration items instead.
Spirit Visage is a powerful item on Vlad, increasing all of the aforementioned healing by 20%, giving him 10 AP due to his passive and giving much needed 10% CDR. However, this item is ill-advised if Vladimir is ahead as it doesn't significantly increase his damage, and he already has massive sustain with just a Hextech Revolver.
Haunting Guise is a good item to buy thanks to Vladimir's high base damage. This item will provide Vladimir with 15 magic penetration, 30 ability power, and 235 health thanks to his passive. This can be sold later if the game goes really long for a better item or upgraded later into Liandry's Torment giving 57 ability power and 370 health instead of 50 ability power and 300 health.
Rylai's Crystal Scepter is a great item for most casters, but Vladimir will benefit even more from it due to his lack of CC and range as well as his passive: it will grant 540 health / 110 AP beyond the base 400 health / 100 AP. Additionally, the passive gives his spells constant slows. Due to Vladimir's low cooldowns, he can also stick easily to most champions, especially if he has movement speed quintessences.
While this item may seem to be a bad purchase due to the mana regeneration, Morellonomicon has 20% cooldown reduction, high amounts of AP, and the passive, allowing Vladimir to hinder enemy's sustain. It is extremely cheap and cost-efficient, and as such, it is a viable purchase on full AP builds, despite the mana regeneration.
It is possible to build Vladimir as a tank or an AP bruiser. Be wary that without heavy AP, Vladimir's damage decreases drastically, especially since Vladimir gains way more HP by building AP than he gains AP by building HP. Therefore, this build is inferior for carrying games, but is viable if Vladimir is behind or if his team already has a mage and instead requires a tank champion.
Abyssal Scepter is extremely good on a more tank-focused build for Vladimir. Not only it increases his own damage, but it offers an aura that benefits at least Vladimir himself, while reducing the enemy's magic resistance (which itself already benefits Vladimir a lot). It also offers health due to Vladimir's passive.
If you don't want to rely on Hextech Revolver for sustain, a Warmog's Armor will do the job very well, while providing Vladimir a good amount of AP due to his passive. Just be wary of opponents with abilities/items that do health-based damage, such as Vayne.
While Lich Bane may seem to be a good item due to Vladimir's low cooldowns, they are so low that Vladimir will rarely be auto-attacking late-game. He doesn't need the extra power from Lich Bane's passive and the mana is wasted.
Rod of Ages offer health and AP, but the mana is useless. This item also offers nothing aside from AP and HP. Rylai's Crystal Scepter is a much better choice even though it offers less health, as it offers a passive that slows enemy champions.
Hextech Gunblade is a bad item to get simply because the AD is completely wasted. The lifesteal may seem like it will increase Vladimir's sustain, but health regained from lifesteal scales with how much damage Vladimir does with auto-attacks, and because he will not be purchasing any AD items, and he has low base attack damage (not to mention the enemy's armor), the health regained from lifesteal is very small. Not to mention this item is more expensive than Will of the Ancients. The active from Hextech Revolver is actually useful, but Vladimir is better off purchasing a Rylai's Crystal Scepter.
Nashor's Tooth may seem to be a good item for Vladimir due to the ability power and cooldown reduction. However, Vladimir is not an auto heavy champion, and the item's passive and attack speed is a waste. In addition, his auto attack range is very short and his spells have longer range than his basic attacks. Besides, there are more viable cooldown reduction items such as Will of the Ancients and Spirit Visage, and Vladimir can max his cooldown reduction with proper runes and masteries.
Some champion abilities can reduce health regeneration such as Impure Shots.
Early game, stay just out of range of his Transfusion. If he uses it on a minion run forward to harass before his Transfusion cools down.
Vladimir lacks any hard crowd control to interrupt channeled abilities, but watch out as his Sanguine Pool allows him to avoid abilities that have effects while channeling (like Death Lotus) or he can time it to avoid channels that have an effect at the end (like Absolute Zero)
Vladimir is one of the most powerful champions at late game, as he becomes virtually unkillable, with overwhelming damage and can wreck past an AP mage's normal counters, fighters, if he is able to reach this point defeating him proves extremely difficult.
However his late game dominance has a cost, an awful laning phase, with Transfusion having a long cooldown, low damage and healing until rank 3-4, step in to harass right after he uses the skill to farm, his only counter-harass will be Tides of Blood which doesn't deal much damage if not stacked and damages him
Vladimir lane weakness declines by the time he gets his Hextech Revolver as he will be able to heal every attack launched against him, if he is not able to farm properly this item will become delayed and he will remain weak for teamfights
Focusing Vladimir in a teamfight is not a very good idea - he is very tanky due to his passive, he can restore his health quickly and lose all focus with Sanguine Pool.
Trying to kill him takes a long time if he is properly positioned and can distract your team from other key enemy targets such as the ADC and assassins.
If you fail to kill Vladimir late game and he escapes he will be able to fully restore his health with minions and jungle monsters without going to back to base.
Do not underestimate Tides of Blood late game, especially if fully stacked. Average late game Vladimir can dish out from 450 - 540 damage, pre mitigation, from Tides of Blood to all surrounding enemies. With some cool down reduction, he can spam this spell continuously and easily wreak havoc if left unchecked.
Try to harass Vladimir into using his Sanguine Pool early in a fight so he takes more damage from it and cannot use it to escape focus fire. Vladimir will use 20% of his current health whenever he uses Sanguine Pool, so if you force him to use it, you've effectively won the trade.
Remember that Transfusion doesn't heal Vlad until the particle returns to him, and because the animation is two-staged (impalement, then return), most single-target projectiles like Two-Shiv Poison, Vorpal Blade, and Null Sphere will generally hit him before he's healed. This is useful to remember should you be uncertain about last-hitting him.
You can use Quicksilver Sash to remove Hemoplague (which is usually paired with Ignite) if he uses it on you. So buying it against Vladimir is a good and rather cheap counter.
Due to his passive, he gains health as his spells grow more powerful, however this leaves him vulnerable to health percentage damage items and abilities (e.g. Null Zone and Blade of the Ruined King).