Teemo - The Swift Scout
Fast, can outrun most enemies if he sees them in time
Mushrooms uncover the map, with enough mushrooms you can have an escape route planned.
Fast attack speed, very useful with lifesteal can solo enemies quite well.
Relatively weak armour, quite easy to gank
Part 1 - Summoner Setup
First of all here's my recommended build, The offensive tree is mainly what you want to be looking at, after that remaining points are down to preference. I will explain further below.
Deadliness: 3, Cripple: 1
Sorcery: 4, Alacrity: 4
Archaic Knowledge: 1, Sunder: 3
Brute Force: 3
Lethality: 3, Improved Rally: 1
Good Hands: 1, Perseverence: 3
The focus of these talents is to increase attack speed and armour penetration, and general damage output, the 6 remaining mastery points have been placed in utility to help the levelling process slightly and to increase mana regen.
The two spells I like to use are Exhaust and Rally, the two masteries above also compliment these. The reason is simple, you exhaust your enemy, pop rally which helps you hold your ground with healing and increased damage, you will 9/10 times kill them if they dont have flash.
Part 2 - Items
Item building depends heavily upon who i'm laning against, and wether it's solo mid or in an outer lane with another team member.
The first item I will always get is Vampric Scepter. This allows you to hold your lane for a long time while killing creeps and harrasing your opponent.
From here I will either save for the B.F. Sword (if I am with a weak opponent and not taking much damage) or I will get Berserker's Greaves for increased attack speed (if taking heavy damage or against a tough opponent this will increase damage dealt and lifesteal return).
Either way the items I recommend building towards are
Madred's Bloodrazor (or a second Bloodthirster)
by this time the game would normally be over as this is alot of gold, but if your still going, I would then get:
This list is not definitive, you can swap out a few things ie for more magic resistance or armour, depending on the damage you find yourself taking. Generally I prefer as much lifesteal as possible, as your high end damage will be dealing 400+ and 25%+ lifesteal will be healing you quite efficiently in team fights or solo.
With the above I have managed to solo turrets and inhibitors behind the enemies backs and pull round seemingly losing games for the win.