The point of this build is to maximize Blinds Ability
Flash (really a must with any champion)
Exhaust (works well with Blinding Dart. Can get over 7 seconds of blind end game)
Teleport (I don't use this because of good lane survivability I will be going over)
Ignite (Works great against healers, and the extra damage is nice)
All other spells not worth having on Teemo
Starting Items: Dorans Shield, 1x Health Pot.
Dorans Shield adds great survivability early game. Gives 120 starting health armor, and health regen. Overall great item.
Next grab boots. Not berserkers, just boots.
Malady (if i don't have enough money i my first trip i grab dagger, scepter, dagger, then malady itself)
Boots of swiftness (Many Teemo players think it's a sin not to grab berserkers, BUT swiftness are much cheaper, stack well with Move Quick, and let you get your dps items faster)
The next item is a situational item. 9 times out of 10 it will be wits end. Let me explain when you won't get this item. If you have gotten this far and lanes haven't broken then the game is going wrong. Needless to say if 1 person in your lane doesn't have mana pass on Wits End for Last Whisper. I also pass on Wits End if there are 2+ ppl in the game without mana. If the other team has Mundo Kat and Tryn, Wits End becomes a worthless item.
Phage (Adds survivabilty and a slow)
If the game goes this far grab a BFS and go Infinity or Bloodthirster.
Blinding Dart will be your main attack early game. Use it wisely because it costs a fair amount of mana and you will have little to no mana regen.
Save Move Quick to escape after flashing away. If you have to go back to heal/buy make sure you're lvl 4 and have this ability to get back to your lane quickly.
With this build Teemo's mushrooms are best used as wards. Place them in frequently used bushes to see where the enemy is.
Gank early, gank often. Ganking wins games. This is another reason you grab boots of swiftness.
Grab buffs as soon as you finish malady. Just place a mushroom in front of Golem or Lizard and you'll finish them off quickly. You can solo dragon around lvl 8-10 so do it. Don't solo baron. You're all about attack speed and with the recent update you'll be dead before you knew what happened.
You are not invincible with this build! You can pretty much take anyone 1v1, but and disable pretty much does it in for you. Play carefully!
Glyphs CD Reduction
Seals HP per level
Marks Crit Damage
Quints Overall HP
21/0/9 is my build, but 9/0/21 is also good
Feel free to ask questions if I missed anything. Feedback welcome