When playing Teemo not in mid lane, an easy way to get First Blood is to use Camouflage just out of range of their turrets' sight or at the edge of the bush closest to their turret, and wait for the enemy champion to start farming. When they move about right next to you, Ignite and kill them with the help of the mid lane champion if necessary. Exhaust would be useful with this strategy.
Blinding Dart with Exhaust can destroy a champion who relies heavily on physical attacks like Tryndamere or Caitlyn. Apply blind first, then apply Exhaust after the blind has worn off. This will allow your blind CD to refresh while your enemy is exhausted, minimizing their DPS. If you use both at the same time, the blind will override the attack damage/ability power reduction. Similarly, you can use these two abilities on two champions, effectively taking them out of the battle for a few seconds.
Blinding Dart can be used in-between autoattacks, which allows 2 rapid-fire attacks. This is extremely important to learn how to use throughout the game. Opening with a normal attack, immediately using Blinding Dart, then proceeding to autoattack will apply great burst damage, even during laning. Try mastering this combo to use it on the fly and you'll increase your ability power/attack speed damage tremendously.
If Blinding Dart is used on Fiora before she activates her ult Blade Waltz it will stop the damage from the attacks but the on-hit affects will still apply, this will dramatically decrease the damage taken. This also applies to Warwick's ult Infinite Duress.
Placing a Noxious Trap or two behind the first turret and before the 2nd near the paths to the jungle but not in the minions' path can turn an almost kill into an easy kill.
Teemo'sNoxious Trap can be used to farm creep waves very effectively; it is best to keep your mushrooms spread out and not too close to each other. If a lane has enemy minions stacking on each other (especially the ranged minions), pop a Noxious Trap down in the middle of them and watch them all die in just a few seconds. Use this only if you need to stop a wave immediately or stop future waves, because it is necessary to maximize potential damage by increasing the number of active shrooms on the map to win. More shrooms = more chances of hitting them = more net damage.
Put a Noxious Trap at key locations on the map, such as by the Dragon or Baron Nashor to reveal when your enemies might be attempting to kill them or to prevent opponents from ganking and make counter ganks. This is similar to a Sight Ward but the range that Noxious Trap reveals is much smaller. (Pro-tip: Place 2. One near the opening and one behind the monster. The front one will explode after an enemy steps on it, thwarting them from starting Baron or dragon, while the back one will allow you to see the health of the monster and whether it is being attacked)
Depending on the enemy teams melee/range makeup, you can put a Noxious Trap to the side of Baron Nashor to reveal 1 or 2 enemy melee champions, or you can place them a little behind the side of the baron if there are 3 or more. This will usually reveal enemy melee champions currently attempting to slay Baron Nashor.
Put a Noxious Trap inside brushes and entrances to your lanes or your team's side of the map to ensure maximum safety.
When laying down Noxious Traps in the jungle, keep in mind that the champion movement pathing often hugs the terrain as they take the shortest route to the selected location. Laying traps against walls at turning points will increase the chance enemies will run into them on their way to/from lanes. Placing down shrooms in the center will allow for a more permanent ward (sometimes).
Also, when laying traps in a lane, remember that minions travel through the middle, and if the front minion runs into it only he and one minion behind him will be hit. Placing them on the sides can increase the chances of hitting a champion.
Placing two to three Noxious Traps by the enemy red or blue buff is generally a good idea considering you might just get lucky and steal it from them while slowing their farming down.
It's sometimes a good idea to place a few Noxious Traps behind you before entering a teamfight, that way if you begin to lose, your team can run off and lead the enemy right into a minefield.
If planting mushrooms at Dragon or Baron Nashor, they will provide vision if placed off to the side.
Don't forget that Noxious Trap can be placed down in team fights and only has a short time to arm (1 second). Doing this could secure a kill or slow down a enemy when he/she is trying to escape.
If you are suspecting a possible towerdive from an opposing champion, place Noxious Traps behind and in front of your turret in order to slow and deal damage to the enemy.
If an enemy is engaging you at melee range, Noxious Traps can be used to peel them off you by placing one underneath you and stepping backwards.
Early on, items like Wriggle's Lantern and Phage will increase your damage output and sustainability and allow you to shut down the enemy top laner. Phage also builds into Frozen Mallet, a very powerful item on Teemo that allows him both to chase and run away from enemy champions with ease when combined with Move Quick.
Magic penetration will apply to already existing traps. Buying items such asVoid Staff or Haunting Guise will greatly increase their damage, even if they are bought while you are dead.
Teemo can build ability power and attack speed with items that proc on-hit effects, like Wit's End or Malady. These combos work well with his poison's on-hit effect.
Building a Lich Bane on ability power Teemo can lead to huge bursts of damage.
Nashor's Tooth does not benefit much into Teemo's on-hit damage. Nearly any other item will increase your damage output for less gold. Malady, for example, deals 20 bonus damage on hit as an item effect, and gives 25 ability power, causing Toxic Shot to deal the exact same amount of damage. However, it increases your damage because of the magic resistance reduction effect, which benefit all other on-hit effect items you currently have while costing 790 gold less.
When facing AP build Teemo during early game, they will typically poke and run, letting their poison deal damage and lowering your health gradually, until they are able to burst. Be prepared to pull away if he approaches, and use Health Potions to keep your health high.
Do not chase Teemo if he attacks once and then runs, particularly AP Teemo, as he is most likely luring you through a field of Noxious Traps.
Because much of Teemo's early game poke is damage over time, the Unyielding mastery is more effective in decreasing his poke damage.
If you are using a champion whose damage output is either strongly or entirely based on their auto attacks (ex. Talon, Vayne, Quinn, or even Teemo himself) you need to purchase items to mitigate Teemo's Blinding Dart