War Criminal Teemo is a very special boy. Your shrooms will easily chunk someones health as soon as you get a Liandries and Rylai's. The build is named war criminal for the stupid amount of damage you do and the statis effects that you apply.

Laning Phase will mostly be you playing relatively safe and trying to CS as much as possible. Poke your laner if they over-extend but don't leave yourself open to a gank. At 6, clever shroom placement at jungle choke points can ensure that you see most ganks coming your way. Kills and objectives are not the main focus of your early game and instead you should be trying to get through the build path as quickly as possible (this does not mean you shouldn't abuse your enemy laner if they step-up).

Mid Game is mostly about you controlling most of the jungle. Right now, you should about 15 Dark Harvest stacks. Your blinding dart isn't powerful enough to one shot someone at this point, so you will need to pretty heavily rely on your shrooms. Place them around the map at choke points, plant locations and objectives to ensure that the enemies have the least fun possible. You should be touring around looking for kills, CS and Dark Harvest stacks to complete the build as soon as possible. At this point you should consider your lane a base of operations, don't stay there all the time but also don't abandon it.

As soon as late game roles around the focus changes once again. You will notice that your autos do 1/15 of a tower's health, but that your blinding dart pretty much one shots squishy targets. The enemy team should have sweepers which reduces the effectiveness of your mushrooms, but odd placements at choke-points will still net you some easy kills on retreating targets or unsuspecting victims. You should aim to finish the game at this point as you have the damage to kill most enemies.

At all points through the game, you should be team-fighting as a mid-liner. Close to the action so you can auto, but not close enough that you're getting targetted. Chuck shrooms into the middle of any team-fight as they will be pretty un-noticable in any kind of chaos. Use blinding dart to make ADCs useless, to secure Dark Harvest stacks and to kill anyone running away.

As Teemo your auto attacks do more damage than many abilities, especially early game. You should feel free to tank some abilities if it means that you can net a dark harvest stack or harass the enemy laner.

Your basic poke combo will be auto-q-auto as this will ensure that they get poisoned if they decide to flash after your blinding dart hits. Shrooms should be placed during fights as they will allow you to proc huge damage in return for a split second of downtime. REMEMBER shrooms do not activate instantly and this should be factored into their placement.

Your Q also has a much greater range than your auto attacks and has a longer range than many other mages poke. Spamming blinding dart is rarely a bad thing as you rarely will be spending mana on your W or R. Your W is only really used in chases or escapes and your ult isn't up all the time.