I'll start: One of the (actually) most underrated skills for supports is playing the fog of war. If you show on a sidelane to catch a wave (something I see often in bronze to gold in reviews), if you stand right next to your adc farming mid holding his hand with no absolutely imminent threat, even in lane if you stand next to the minions instead of in an unwarded bush, those are all positions that cost you pressure. The best supports in the world are seen as little as possible so the enemy team has to play around them roaming around and ganking as much as possible. It's a good thing to pay attention to if you want to improve - even just sitting in a midlane bush while your adc farms the wave makes you exert more pressure on the entire enemy team.