In laning phase, in most cases, you will have a stronger lvl 1 - 3. You want this time frame to poke down the enemy, using your lethal tempo. Defend your minions against the enemy laner from cs'ing. If they walk up, auto attack them to proc your lethal tempo, keep shooting while walking to them if they flee, if they are going all in on you, you want to kite back to your tower, while shooting them if possible. On Teemo, the core thing is to kite, do not get hit by skillshots or cc's, don't get into their melee range, and know they skill cooldowns. For example, Maokai has one of the best engages with his W. If you know it is up, don't fight him unless you have a giant minion wave.
Another thing to keep in mind is to not be overextended without vision. You always want a ward in case of ganks, and also, just don't be overextended. You almost always want to slow push, DON'T MISS CS BECAUSE YOU ARE TOO BUSY AUTO ATTACKING THE ENEMY. Cs is super important, and you don't want to miss any. Remember, about 18 cs is equal to a normal kill, which is 300g. If you are against a bad matchup, ALWAYS ASK FOR GANKS.
Anyway, if you are against hard all in champions like Renekton, you want to always play safe, don't get carried away because you want to poke. Focus on cs and get your items to fight them. Since in laning you will not level Q, it will be on cooldown most of the time if you use it for poke. You don't want to do this, it doesn't provide much damage, and is crucial for defending yourself if they all in you. The blind is so amazing versus AA based champions.
Since Teemo is a squishy champion, you will get punished harder by minion damage than most top laners, if you draw minion aggro, go in bush to drop the minion aggro. Don't poke if they have a giant minion wave.

Those are my tips to laning as On hit Teemo.

As always, there are team fights. Teemo is decent at team fights, especially with blinding their ADC. As on hit Teemo, you want to always kite against assasins, and deal damage to whoever is in the way. You might not be attacking backline often, since your range is shorter than ADC's auto attack range. Your objective in teamfights is to just keep autoattacking, if you are getting focused than obviously your tank isn't doing a good job. You don't want to drop shrooms in the middle of the teamfights, it doesn't provide much damage.

Basically 2 things to remember, blind ADC(or whoever does a lot of damage with AAs), and kite.