Attack a tank with e and only with q when he comes close. If the enemy is mage attack with q and basic attack then run back and repeat.Watch out for minions! Sometimes when enemy has low health flash than q and ignite him at the speed of lightning and you got yourself a kill.

Attack pantheon with e 2-3 times if he trows q on you because he can't trow that much spears how much you can hit him with basic attack. And always carry a lot of hp and some mana potions to keep harassing him, because if you don't pantheon will just q you 2-3 times than do his combo, this proves that Pantheon is bigger gay champ than Teemo. Same goes for Vladimir, he can't heal with his q that much to cover all damage you done to him just pressure him. Akali will most of the times go mid but sometimes top. You have huge advantage until lvl 6, than you have to buy Banshee's Vail and spend 100 gold on pink trinket or wait lvl 9 than upgrade your yellow trinket to pink trinket(so you can see her when she trows the circle). Same with Fiora, harass with e then q when she comes close, but the difference is that you rush Zhonya's hourglass so when she uses ulty you activate it.

Don throw and go 1 vs 5 or similar ****. Only go for kills if you can get away with it. Stay with the team and stay behind the tank. Always wait for the tank or somebody else to initiate the fight then you concentrate on ad carry or ap carry. If you can't reach them attack the first enemy you come across. Ward bushes, paths, dragon and baron with mushrooms to prevent ambushes and help your team. Alway put mushrooms near turret also so you can defend it in case of 1 vs 3 scenario.

Make ambushes and come at enemy from behind to kill him fast and easy. Now how to make perfect ambush. You need to place your mushrooms correctly on the map. Put one mushroom where minions wont go in but player will, little to the left or right from minions path, than put one where you are invisible, because if the target is melee he will maybe try to attack you and there for activate the second mushroom. After the target has stepped in the mushroom q and e(2-3) times would be enough to kill him. Experience will help you with this because I have over 500 games with Teemo.