This build focuses on AD DPS Teemo. He is really good at harassing early game. Go in the middle of the lane (if they aren't there in the bush or anything) and go invisible. When they come close enough hit them once or twice with basic attacks and walk back a little, then minion farm a little and try to go invisible again without them noticing. When you have blinding dart and you're in bot, you'll be against the AD carry (in ranked or draft) so when you come out to harass hit them then blind them and try to hit them again so they can't retaliate because of the blind.

Watch this video and you should know how to play Teemo pretty well. Play Video It gives you the whole thing about Teemo and tells how to level up the moves.
Have fun rocking all the lanes!

I choose cleanse for that pesky Ignite early game. It can save you from death from Ignite and late game keep you from getting stunned or snared or anything.
I take Flash for a few reasons, it can help you flash into the fight and pick up a kill or get there faster, you can use flash to catch up to kill an enemy, or you can use flash to get away.
Exhaust is a great summoner spell you can take instead of Cleanse if you want to, you can use it as they run away to slow them down or as they chase you so they can't catch up.
Ignite works too instead of Cleanse for the early kills and for keeping health regeneration down. Ignite is good for any lane to do that last bit of their health.

I take the Armor Penetration runes because this is an AD Teemo build. The health per level seals are to build health through the game and into late game. The magic resist seals can help you stay alive from all the casters. The flat health quints are nice for health early.

Pros
-Exceptional Harass
-Mushrooms are built
in wards
-High movement speed
from Move Quick
-Renders enemies
helpless with blind
Cons
-Rather squishy early
-Mushrooms have small
sight range
-Movement speed reduced
by enemy attacks
-Blind only stops basic
attacks from hitting

Doran's blade is for the early laning damage. Beserker's Greaves are to start out the attack speed you build more and more through the game. The next item is either recurve bow or you can go for bloodthirster first with vampiric scepter. If you need the early life steal put vampiric scepter then bloodthirster in front of recurve bow and wit's end. Then you get malady for more attack speed. The frozen mallet for some extra health and damage. Madred's Bloodrazor for farming and late game jungling for gold. And then bloodthirster if you didn't get it before recurve bow.