I see a lot of people complain in pre-game lobby when I hover Teemo. If you think about it though, his kit works very well to counter most ADCs. What do most ADCs rely on? Their auto attacks. What does teemo's Q do? Makes their auto attacks useless. He's very good at being able to ambush behind them from bushes as well.

if you see someone taking teemo bot, have a little faith.

Teemo is all about positioning. If you can catch an enemy off guard, they usually have no chance to fight back. Especially in the bot lane where teemo's Q renders most ADCs powerless.

If you have a blitzcrank or thresh supporting on your team:

Try to place your shrooms in the bush closer to their turret. Have your support pull them into the bush over the mushrooms. They'll have to step on at least a couple on their way out, making them take loads of damage already. If they try to flash out right away though, lucky you, they're going to be slowed from your shrooms for a little bit, so you have plenty time to W in for the kill.

If you do not have blitz or thresh:

Place the shrooms in bushes and kite the enemies through them. Once you are 1 or 2 items in, it isn't very hard to shred through the enemy ADC.

Watch out for supports who have a lot of CC. Teemo may be a power house but is also extremely squishy and can be taken down very fast early game if you aren't watching where you're going.

If you think this could benefit from something else or if you have any other general feed back, feel free to drop a comment. This is my first guide so I don't expect it to be received amazingly.

Good luck with your teemo-ing!