Background info on me: Ex-DotA 2 supp main, average MMR. Current League supp main. Bronze 5 seed this season, currently Gold 5. Got out of Bronze in about a week (played top and mid then tho.) Been a supp main again since Silver 4 (decided to give it a go again after getting bored of Irelia)
My OP.GG Page, for info, if you'd like to check the validity of statements mentioned: http://na.op.gg/summoner/userName=EllenTheGenerous
So, I'm gonna tl;dr the fuck out of this cuz my initial version was too rambley and long. Basically, it's about picking your support, demoralizing* the enemy early on, and playing to YOUR strengths (AKA early game). Your damage is strongest early on, and you will be able to outdamage even ADCs and Mid-Lane mages as of right now. You have high bases, low scalings, and scalings on your utility. You should be aiming to make plays whenever you feel able to, which should be at least once every 30 seconds. Try to land a bubble, try to hook the adc, etc. Playing passive as a support is honestly unacceptable until the enemy is too far ahead, which take forever to actually happen. You should be willing but not trying to take kills. Use all your shit and then some when making plays. Diamonds are a girl's best friend? Auto attacks are a support's best friend. They add up HARD.
Basically, what I'm saying is, abuse the everloving fuck out of your early damage and utility to take control of the lane as early as possible. You should be able to have complete lane dominance at level 2, no later than level 4. If you lose this, its YOUR job to get it back.
As a support, YOU are the carry of the early game. YOU are the one who needs to make the plays, YOU are the one doing the damage, and you have to do that while making sure both you AND your ADC are safe.
*When I say demoralizing, I mean constantly poking the enemy adc out of lane type of deal, nothing to do with chat. Laugh spam is good if you're Lulu, too.