Dark Harvest is your life. If you see red get it. Your only goal in laning phase is to get dark harvest stacks. If it costs you your life or your adc's then that's part of life. If people tell you your inting, it's because they don't know how to play Teemo. They may also say that dying isn't worth the small quantities of bonus damage. In this sense they would be wrong as well, because, dark harvest also gives a satisfying little pop when it triggers, not just damage.

Many people go into the support business because they want to do good in the world. This is probably not you, if you want to play Teemo support. If it is, just go and play Soraka. The other majority of support players play support because they can't cs,like one of the support champs,or are in a duo. If this is the case then you should enjoy Teemo support. All you do is sit in the bushes and wack the adc or support. If you AA-Q, then you should deal more damage than them at first and make their life miserable. This is your only trade in lane other than just AAing them.

A lot of people wont enjoy playing with a Teemo support. (or in any other lane.) The easyest way to make sure you don't get reported is to just be really nice. In champ select ask if they're okay with Teemo support. (you can pick it no matter what, but they normally say yes, and feel better.) After you ks with poison or a shroom, apologize, and they wont get as mad when you ks the second time.

Late game, I only have two pieces of advice: 1 Take the buffs, it doesn't matter who you take them from, because they are tons of fun to have. 2 Fight everyone, cuz it's lots of fun to solo kill adcs.