Depends on the champ your going against, if it is an aa heavy champ, like riven, yas, master yi, trynd, then use q. Otherwise, use e.

As a Teemo, your mushrooms are very important. If your opponent has a dash move, lure them in to dash at you, but actually place a mushroom in front of you. This is effective, and then go all in, for yasuo, place mushroom right below you, and when yas uses his ult, he will go to you (if your airborne), and then smash down to where you were, so the mushroom there is effective, add ~2 for the damage, and then go all in, with corrupting potion. Remember to put 2 mushrooms in the bush down the river and one thats around the krugs place, if you dont know, just place mushrooms where you think you might get ganked from.
LOOK FOR PATTERNS. If you opponent goes into bushes a lot, then put your mushrooms in the bushes, and dont forget mushrooms can jump on eachother, enabling you to put mushrooms into all 3 of the top lane bushes in one bush

Some Teemo mechanics that you may have not known.
When teemo's passive is activated, he gains an attack speed boost. Most people I see play teemo don't abuse this fact, that at level 1, you can turn invis in a bush, wait till the enemy top laner arrives, and then just first blood very quickly, due to his increased attack speed for 3 seconds. so turn invis, use your q/e depending on what you started with, and then DESTROY the enemy toplaner.

You can use Teemo's q if the enemy is on the front half of their turret and run and not take any turret damage.

Go Nashors tooth first, unless your against a vlad, dr.mundo or anybody that heals. If the person heals, Get Morellonomicon as your first item. Usually, I go Nashors Tooth, sorcerers shoes, Liandra's Torment/Void Staff/Zhonya's hourglass depending on the situation.

I hope this guide has helped you, and if you did enjoy it, please share it. Now, I share this passion for teemo, I don't know why but i love this champ so much. IDK
Hope I helped, and Never underestimate the power of the scouts code ;)