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.
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 ganking and make counter ganks. This is similar to a Sight Ward but the range that Noxious Trap reveals is much smaller. (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 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.
Liandry's Torment combined with Noxious Trap deal massive amount of health burn, up to 4% per second per mushroom. The base amount is 2%, 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 20%. 4 seconds of doubled damage totaling 16% and 2 seconds of normal damage continuing after the poison expires totaling 4%.
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.
Alternatively, you can set up Vision Ward in the strategic place where you think Teemo will place his Noxious Trap. You also can attempt to bait him into taking out your Vision Ward in order to engage a fight.
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. 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.
Oracle's Lens is a great counter to Teemo, revealing and disabling his traps whilst giving you true sight for ten seconds to sweep out even more mushrooms or see a camouflaged Teemo.
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's Lens if necessary.
Yorick is considered to be a strong counter to Teemo for many reasons. First, his passive, Unholy Covenant mitigates a lot of Teemo's poking harass, including Toxic Shot. Second, Yorick is able to out-sustain Teemo with his Omen of Famine. Third, his kit functions more of a ranged AD caster rather than an autoattacker, thus making Teemo's Blinding Dart useless. Finally, Yorick can use his ghouls to safely detonate Noxious Traps in a safe distance, thus denying Teemo lane and map control.