Support teaches you more than just map awareness and aggression. Most folks don’t realize how much I’m actually doing, and I frankly hate this idea that support are the least vital in a game – everyone is vital, and anyone can lose the game for the whole team. A bad support can lose you the game harder than other positions, because you lack proper/any wards, lack judgement calls, lack awareness, lack AD farm, etc.
Cooperation. You need to be sure when you’re going to get a kill, when to exchange, and work with your AD so they know as well. Make sure they know when you’re harassing, when it’s time to go in, etc.
Map Awareness. Jungle teaches map awareness, but part of my job as support is to also watch other lanes and let them know about incoming ganks. Everyone, no matter who, gets “in the zone” and doesn’t notice that Ahri hiding in their bushes – I have the time to check other lanes, so I do. Also, proper warding.
(EVERYONE SHOULD FCKING BUY A WARD, not just the support. Top needs it for river/tribrush to avoid ganks. Mid needs it either on river or near wraiths to avoid ganks. Junglers can add a ward above river while mid has a ward below to provide complete jungle exit coverage. When you go back, buy one ward. Easy.)
Harass/Zoning – Being aware, not only of your own zones, but how they overlap with teammates, is key to harassing safely and zoning people from XP, even with a Soraka. You need to know when it’s safe to harass, who will win the exchange (based on damage), and make sure you’re the one winning.
Making Calls – Often the support is the one making calls for when to do dragon, when it is safe to baron, where people are or where they were last scene, thanks to our ward coverage, map awareness, and CV. You need to be confident and in control, and if your team is being stupid and not taking free dragons, make them.
Reading Players – This is part of harass and part map awareness, but after a while sitting watching an AD carry and support, you learn people’s tells very quickly. Sudden aggression/moving past the point of safety? Their jungle is near. Sudden movement in one direction? Cait or Graves are going to Q. Count Cait’s shots until headshot, and taking the shot for your AD.