The only part you really need to know about Teemo, is to always take pot shots at your lane opponent.. at any time possible. Your poison means that a single auto attack will do insane dmg over time. So while farming minions.. if you dont see a last minion hit in the near future.. run and take a quick hit on your enemy.

Always make sure to give your self a "way out" meaning if you want to over extend while farming.. set mushrooms in a path where you can easily run to incase of a gank. Such as small aisles where they cant possibly miss your mushrooms. And you can "W" to safety through them.

Use your mushrooms as wards in bushs and in the river.. It is very hard to gank a teemo that properly mushrooms his area.

Green Mushrooms = Impossible to be ganked
Red Mushrooms = Full control of their blue, once completed - makes for an amazing trap.
Purple Mushrooms = Full Baron Control, force a fight at baron with those mushroom placements and you will win.

If you notice that the enemy is getting alot of magic resist. Buy an Infinity Edge as your last item. With your attack speed, you can easily become an AD champ at any time.

The first build is the most aggressive and probably successful build. The second build is an APAS Teemo, getting rod of ages first and zhonya's makes you a little tankier and able to get out of bad situations while also making your mushrooms much much stronger. The downside is that you lose the madred's blood razor for tankier champions, and you lose the ability to be a hybrid.