Why ignite and exhaust, Well move quick gives you enough plenty of time to escape, If you can't escape you over extended or got slow and cc'd a **** ton. Ignite = crazy DoT with you're poison combo with exhaust hello first blood and gg.

I love to start with poison purely because it helps with your cc and the killings of enemies, Move quick for the harass and escape. Normally I don't get blinding dart til like level 10 which thats when I enter most teamfights.

The items are similar to example solo mid rainmans, But that doesn't matter it works so use them. Tweak them if you want i personally prefer these.

Magic Resist
Banshees
Hexdrinker
Wits End
http://www.mobafire.com/league-of-legends/item-purchase-planner#&item=112-68-76
Armor
MADREDS. Thats pre much all you'll need
If the possibility you need more.. well get thornmail duh.

Pros: Huge Dmg
Mushrooms for warding, lane control, damage
Move quick is like a mini ghost
He's ****ing fast in general
Blinds
Poison
Kills Minion waves in no time mid game
Put frozen mallet on him he becomes god.
Cons: Low Hp. He's basically a global taunt, Everyone wants him dead.
Low CC Hence why you get frozen mallet plus HP which he NEEDS

Teemo can rip apart tanks in no time, but you NEVER go for the tank firsts thats stupid, go for the melee unit first then ad carry then tank. thats what teemo is good for remember to always knock out the biggests threat before attacking the melee.