Hello I am a the filthiest person you can imagine on league, a teemo main. How ever, you are not here because you hate teemo, but because you wish to learn him.
I am a gold elo teemo player, I just picked him up this season as a main, but I have been playing him since I started playing league shortly after reksai's release (back when teemo's blind poisoned as well.)

Normally I will take flash and ignite. This gives kill pressure throughout the whole game, whilst still having an escape.
Against a pantheon I will always take teleport because HE WILL **** YOUR **** UP. This is not an exaggeration. I will expand more on the match ups.

WE DONT GOT NONE NO MORE

SEE NOTES ON RUNES< WAS TOO LAZY TO PUT IT HERE

On-hit teemo always needs these 3 things: attack speed, slows, and on-hit damage.
Items to never get:
Tri-Force- because you never proc the sheen, and the stats aren't the best for this teemo build.
Archangels staff- you will never get the upgraded version, also, it offers no useful stats to an on-hit teemo.
Protobelt- just, just why :(
Void staff- this is on-hit, not ap, you hecker.
Sunfire/bamis- you are a ranged chanpion, why would you get an item for melee tanks?

If its a melee top, poke the **** out of them, once you get them low enough just flash e q e ignite. boom. that is the lane until level 6

If ranged top, just poke when you can, and try and get an early kill.

Once you hit level 6 start placing shrooms for vision, or you can use them to push waves, more info in shrooms section.

If you haven't taken turret yet, then just start roaming to help pressure the map.
If you have taken turret, see above ^.

Yasuo- easy armor
Darius- easy armor
Garen- easy armor
Illaoi- easy armor
Aatrox- don't worry about ever seeing him
Jax- hard: you should avoid his engages, just farm and poke from a far, armor
Renekton- Hard: crocman hurts a ton, build armor and avoid his E W Q E combo
Olaf- hard: try to avoid his q, be aware of his early all in, build armor and avoid trading
Malphite- Easy: if he is tank, otherwise you should afk or force mid to trade. build magic resist and armor against him
Nasus- Moderate: NOT A DIRECT COUNTER TO HIM, so you have to play lane smart, get an executioners culling and poke him
Trynd: Hard- he will **** ur **** up with his E start
Jayce: Hard: holy moly he pokes hella hard

HOLY **** THIS GUY. BAN HIM OR DODGE IF HE COMES UP, YOU WILL LOSE LANE. IF YOU STAY IN GAME HE WILL **** YOU. SWITCH WITH MID IF POSSIBLE.


If this doesn't work here is items: dorans shield 1 pot start. then build goes deadmans tabis BoTRK, then other items to diminish the rest of their teams damage.
Would recommend going full tank against him, maybe one or two attack speed items.

Either use for vision in river for ganks or in choke points in jungle.

Use for wave clear if the laner backs. Simple enough