ALWAYS prepick your best ADC. Chances are that support will go synergy, if not, then try to give good ADC yourself, if not experienced enough yet, then go with your best. Even if you win early game, if you bring unexperienced ADC it will cost your teamfights.
There are 3 support types.
Tanky-CC such as Leona, Alistar, Tresh, Blitz etc.. These guys live for engage, and you MUST follow up. So always pay attention to them, and be ready to engage at all times. If countered with Morgana, or Braum, or Ezreal, then try to play safe, and be prepared for HELL.
Poker such as Brand, Fiddle, Vel'Koz, Zyra etc.. These guys are all about poking the sht out of the enemy, but their trade will unlikely worth it unless you do the same. Best if you bring Ezreal, Caitlyn, or Sivir along. If countered, then stick to turret, and farm/poke from there.
Protector such as Lulu, Janna, Soraka, Yuumi.. These girls are about keeping you alive at all times. DO NOT all in until level6. But remember, that pretty much any trade is auto win, if the support is good. Poke when you can, but if health goes down quickly, then disengage. Also if playing against all-in enemy, then disengage instantly until 6 unless you are very confident to beat the enemy. Best if you bring something with big damage. Your survival will be the job of your support, and not yours. Varrus, Jinx, Vayne are great ones.
Current top ADCs:
Easy to survive with, because of the free flash, but difficult to deal real good damage. Surviving the game is not enough. You need to deal damage, and that takes some practice. Still he is one of the stronger ones with big versatility. He can poke the hell out of the enemy, can easily disengage to be healed, and can give nice all-in on the CC-ed enemy.
Probably the hardest ADC in the entire game since. Ever. But a good Vayne wins lategame. Period. There is no counterplay, no counterbuild, no counter champion for lategame.
Not exactly easy, but a good Draven wins botlane with any support against any enemy. And a fed Draven will win the game easily as well. He still needs skill though.