Teemo is a marksman in the top lane or mid lane witch can either be played ad or ap this build will be focusing on ap because I like to deal tons of dmg u could play him ad but that was way back in s2

When Playing Teemo The first thing u have to do is harass your opponent Hit them with a basic attack and blinding dart this will deal enough dmg to back them away.
When u hit lvl 6 try to place as many shrooms as possible through out the map Specially in front of blue buff red buff or dragon and on the river.
Teemo is an anti assassin champion so if your chased by zed or tryndamere don't be afraid to blind them u will get away.
Try to Lure people in your mushrooms by hiding next to them in stealth.
Teemo is one of the best harassers in lol so don't be afraid to duel specially ad champions.
and never try to solo against a team