Vi fits the role of bruiser very well and should be played as a semi-tank. Abusing your Vault Breaker would be a good harassing strategy as it closes the gap between you and your enemies. Be careful about using this ability as Vi has no other escape mechanisms once Vault Breaker is on cooldown.
Because Assault and Battery does 75% of the ability's damage to enemies between Vi and her target and knocks them aside, try to hit as many champions on the way to the target as possible.
Vault Breaker can be used to dash over almost any wall in the jungle. You can dash over walls to gank unsuspecting players, or, with some right warding, easily catch the enemy jungler off guard. Using Vault Breaker will also allow Vi to reach her jungle camps faster.
Using Excessive Force at the right angle can give you a kill when an enemy champion is behind your target.
Excessive Force can help you destroy turrets faster as it resets your auto attack timer.
As Vi is best built as an attack damage bruiser or off-tank, one should purchase both offensive and defensive items. Items that provide a mixture of both offensive and defensive stats, are most often good choices for Vi.
Trinity Force is a more offensive choice here, as it also gives attack damage, attack speed and critical strike chance. The movement speed increase and Phage proc also make chasing easier.
Iceborn Gauntlet is more defensive, as it offers a large quantity armor. The area damage from the proc, combined with Excessive Force causes massive AoE damage. This is more recommended against heavy AD team. Cooldown reduction and the Movement Speed Slow passive both improve Vi's Excessive Force usage frequency and damage dramatically.
As Vi'sBlast Shield scales with 10% of her maximum HP number, an effect similar to Nautilus' Titan's Wrath shield. As a result, it is best to shy away from pure armor or magic resist items on Vi, and instead choose items which grant a substantial amount of bonus HP as well as a resistance stat. Flat Health Quintessences are a viable option in lane or in jungle for further early durability.
The Black Cleaver has great synergy with Vi's burst combo, allowing her to apply a full set of stacks with Excessive Force and Denting Blows. It also greatly synergizes with Denting Blows's armor reduction, reducing the enemies armor by 40% total. This will greatly improve both your damage, and physical damage dealt by your teammates to the target.
If the rest of the team would not benefit from The Black Cleaver stacks, then note Last Whisper will raise Vi's damage output more with higher % armor penetration.
Vi has no natural health sustain, so investing in large quantities of damage and lifesteal can form a viable carry build. Both The Bloodthirster and Ravenous Hydra have high attack damage and substantial lifesteal, and are great offensive items for Vi. All lifesteal can synergize with Vi's ability to shred armor, as lifesteal returns HP based on the actual damage dealt to a target after Armor damage reduction has been applied.
Zeke's Herald can also be purchased in a durability-focused build. Although it provides appreciably less attack damage and lifesteal than other items, it will help to buff allied units and increase your durability through bonus HP stats.
Wriggle's Lantern is a powerful carry item when playing Vi in the jungle, but is generally less effective for bursty early game builds such as Spirit of the Elder Lizard into Brutalizer.
The Guardian Angel is a good item for Vi's aggressive playstyle, as it will allow you to die once in a team fight. As Vi is a great initiator, she's likely to be focused down quite fast. Getting a Guardian Angel will allow you get back in the fight.
Vi is an attack damage caster but items that grant increased attack speed will greatly improve her effectiveness moreso than most other attack damage casters because Denting Blows will proc faster and Vi's overall damage will increase.
Sword of the Divine provides 45% attack speed and a steroid. The steroid provides 100% attack speed and 100% crit chance for 3 seconds or 3 attacks, procing Denting Blows.
Zephyr can function on Vi when not building Mercury's Treads. The Zephyr offers Tenacity, attack damage, cooldown reduction, attack speed, and more movement speed to chase targets.
Spirit of the Ancient Golem is a great jungling item for Vi, as it opens her build up for any boot upgrade while starting her off with the Tenacity trait that she needs.
Eventually you might want to sell your Spirit of Ancient Golem near the end of long games for a Zephyr, which has the same Tenacity and Cooldown Reduction but with added Attack Damage and Attack Speed for taking down turrets as Vi.
The Howling Abyss
The Crystal Scar
The Twisted Treeline
Vi relies heavily on crowd control to win 1v1 fights or 3v3 fights. She can easily disrupt enemy lines with her ult, and this will give her teammates enough time to back her up. Scattering is a good way to prevent Vi from knocking you aside or dealing massive damage with Excessive Force.
Since Vi has no other natural way of sticking to enemies after she has used Assault and Battery and Vault Breaker, save your crowd controls or escapes until after she has consumed these abilities, especially since Assault and Battery makes her immune to crowd controls as it is being cast.
As Vi is a powerful bruiser, making sure to pin her down and not letting her get the core items she needs would give you an advantage against her team as she would be too soft to initiate and her damage output would be very low.
Not letting Vi proc Denting Blows is crucial for lane control and poke, so watching out and avoiding a Vault Break can often decide the fate of a skirmish (being CC, a Denting Blows stack and gap closer).
Early game Vi can easily be pushed out of lane by controlling her shield procs and attacking after it expires if she uses Excessive Force to farm.
As a jungler, one of Vi's biggest strengths is her ability to win 1v1 duels thanks to her Blast Shield and her ability to punish tank junglers with her Denting Blows. Therefore, avoid playing tank based junglers like Volibear, Amumu, and Rammus.