So this is just a quick guide on how to get First Blood with Teemo, 95% of the time, in 5v5 matches.
Teemo is a popular choice for many players, so not only will I go over how to play him early-game, but how to defend and play against against him as well.
So first off you want to buy your initial item, I usually go with a vampires sceptre, and a Mana or health pot. For summoners abilities, I generally go with Flash and Ignite, as this gives me the extra damage to stack with my poisoning capabilities, as well as a chasing and escaping ability that has a fairly short cooldown.
SO now what you've been waiting for - how to get an easy first blood and set yourself up for the rest of the game.
The most important thing to do is to be fast. You've got to get your items within the first few seconds, and run to the middle lane as fast as you can. Now the ability you want to get is his first one - poison dart. This gives him a blinding ability, which does some nice damage on top. Now if you've done this right, you should have your items, be in mid, with your ability ready. Use your passive to your advantage - before the opposing champion gets there, go stand near their side of the map (not too much or else they can run to safety) and wait until invisible. Then simply wait until the opposing hero runs past you, and attack them.
This is the important part. You want to get 1-2 hits off them before they can notice you and retaliate, and when the finally get around to attacking, pop your dart and get another few hits in. By then you should have had around 4-5 free hits, without them damaging you at all. Then you simply need to finish them off, using Ignite or another ability if you have to.
And there you have it - how to get First Blood with Teemo 95% of the time. I use this every game, and it usually wins us the game if I can get it.
Now to how to play teemo early game. The main thing you need to do is use stuns/armor to your advantage, but not to harass him too much. Let him get cocky, and then flash/move near him, and use all your abilities and power to get him low/kill him. The trick is to not harass him in little bits - because he'll win because of his poisioning capabilities, but to harrass him in single, powerful bursts.
This has been my first game guide, so please don't be too harsh :P
But any comments or advice is certainly welcome.
I hope this helps you to win as Teemo - or defend against him, in future games .