When playing Teemo not in mid lane, an easy way to get First Blood is to use Guerrilla Warfare 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 .
Blinding Dart can be used to harass effectively and can help Teemo kill physical champions in fights.
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 as an autoattack timer reset. 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.
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 Dragon or Baron Nashor to reveal when your enemies might be attempting to kill them or to prevent ganking and make counter ganks. This is similar to a Warding Totem but the range that Noxious Trap reveals is much smaller.
Tip: Place two, 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 Nashor 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 1-2 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.
Make sure to place the Noxious Trap out of the path of the Rift Scuttler or kill it in advance, since it will trigger shrooms.
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. Doing this could secure a kill or slow down an 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.
Teemo can be used to split push; Noxious Trap gives him advanced warning and often weakens enemy champions coming to stop him, Move Quick allows him to escape, and Guerrilla Warfare makes him even harder to find.
Teleport can be used on his Noxious Traps. With good placement, this gives his team the widest range of teleport options possible.
Ultimate Hunter is good on him, as it will improve the recharge time of Noxious Traps, especially as he gets more Bounty Hunter stacks. Reducing the cooldown of shrooms is impactful as it allows for shrooms to be charged faster; enabling it to be planted more continuously.
Arcane Comet can add damage to Noxious Traps; as the comet appears to have a delay rather than a travel time it could hit targets far away about as easily as in close range. Noxious Trap allows him to often trigger the rune even if he is pushing on the other side of the map, maximizing its efficiency.
The on hit damage, attack speed and AP allows Teemo to push much more effectively using only basic attacks, allowing him to save Blinding Dart for fights (as well as conserving mana for Noxious Trap; he could feasibly get away with not building any mana items in this case).
Liandry's Torment combined with Noxious Trap for a decent maximum health burn. The base amount is 1%, doubled when the movement is impaired. The health burn will refresh every poison tick, which occurs every one second. This means the total burn will equal 10% (4 seconds of doubled damage totaling 8% and 2 seconds of normal damage continuing after the poison expires totaling 2%)
Although Teemo has a slow basic movement speed, Move Quick significantly increases this out of combat. Combined with Boots of Mobility and Lich BaneTeemo can move between lanes and get back to lane very quickly.
However, if an enemy runs into one of your traps, you will be in combat. This means the bonus movement speed from Boots of Mobility will be removed.
Luden's Echo is a good AP item on Teemo because it procs when an enemy steps on your mushrooms giving your mushrooms even more damage.
Purchasing Doran's Shield can counter Teemo early game by reducing damage from his autoattacks and restoring health, but bear in mind that Toxic Shot is not blocked. This is especially useful for melee champions who will take occasional harass from Teemo in lane.
When facing AP Teemo during early game, he will typically poke and run while letting his poison deal damage and lowering your health gradually, until he is able to burst you down. 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.
If you are using a champion whose damage output is either strongly or entirely based on their auto attacks (ex. Jax, Vayne, Kog'Maw, or even Teemo himself) you need to purchase items to mitigate Teemo's Blinding Dart.
Most Teemo players disregard building defensive items and are therefore easy to kill. Look for opportunities to engage and burst him before he can retreat to his minefield.
Noxious Traps grants Teemo strong map control by granting minor vision in addition to the strong slow and damage over time makes Teemo relatively difficult to gank after level 6. Coordinate with your jungler before level 6 to shut down his farming and bring Oracle Lens if necessary.