This is one my first guides. This is my Teemo Guide, I started playing Teemo when I first started playing the game. I've always loved how Teemo's abilities compliment my play style.

ADC = Attack Damage Carry
ADB = Attack Damage Bruiser
APC = Ability Power Carry
APB = Ability Power Bruiser
MR = Magic Resist
AP = Ability power

Pros:
MUSHROOMS! -Free Wards, Escape mechanism, Pentakill from across the map, oh and KS Galore-
Blind -Can peal a bruiser/AD bruiser or Carry off your support, or another carry-
Move quick - you can be the fastest champion in the game, great for getting to or running from team fights-
Poison - first blood was never so easy with toxic shot-
oh and Camo! -stand still and you become the hidden threat to the half health Shaco trying to gank your Sona/Soraka

Cons:
-You'll pretty much get focused every team fight
-If you don't have an escape route, you're pretty much screwed
-Very squishy
-Always busy
-Never enough mushrooms >.>

pretty much. Flash is op. and ignite helps getting that first blood, or shutting down life stealers/regeners IE: Mundo, Vlad, Fiddlesticks. Flash and Exhaust are also viable, to further shut down ADCs and ADBs.

Ok on items.
this is MY set up. I want to put out there, if you have a different set up, that's fine with me, this just just what "I" use.

your core items are:
- Nashar's Tooth
- Malady
- Rabadon's Deathcap
- Boots
- Hextech Gunblade
- Rylie's Crystal Septer

With these, you get a bit of Attack speed, MR shred, AP and Lifesteal and Spellvamp, and a bit of healths. Teemo with this set up, can be pretty devastating, you'll be hell on wheels, often dropping people before blinding shot wears off. Oh, and them mushrooms

Mushrooms, and how to use them effectively
first off, you never have enough >< and they're the greatest thing in the game.
- Warding, you should be warding at all times with them.
- Set up a get away, I like to spam mine in my bushes for a get away, or to prevent a gank...
if I get into a sticky situation, I run into my own mushrooms, and try to get my victims, as we'll call them, to follow so they take magic damage, and are slowed enough for me to get away, or pop some free shots on them.
- Zoning - now this is a great thing, I can pop these in bushes and force my opponents out of them easily, being scared of teemo mushrooms is enough for me to zone people out of the lane.
- farming minions, late game, one mushroom can pretty much decimate an entire bunch of minions, 2-3 waves you say? no problem. this is good to remember since you can quickly scoot up and save a turret while your team members push or are in a team fight
- Saving allied champions - Having your guys running at you, while being chased, can turn a gank into a counter-gank in seconds. Drop a mushroom, and stand on it for camouflage, ganker hits the mushroom and you unload on him, dead in seconds with nowhere to run :).
and lastly - Gank-deturrent - this sounds odd yes, but you can actually drop 2-3 mushrooms and stand on them, as long as the ganker(s) see you do this, they won't come near you. just saying, but a pissed off teemo, and 3 exploding mushrooms is enough to make anyone run.