https://www.youtube.com/watch?v=y6bWcmK-w_M
This video taught me how to play support (at least/especially during lane phase). Pay more attention to the mindset/general principles; the specifics aren't as important especially since this was a few years ago and the specifics of the game, ie items and stuff, are very different now. Providing strong lane presence is so powerful; you probably don't want to be going as ham as Aphromoo in that video unless you are way better than your opponents/really know the limits of your champion & their champions/trust your ADC to back you up sometimes, but the principle of zoning and providing presence still applies.
I'm sure you know what it feels like to have an enemy blitz in bottom brush just waiting to grab you; you're basically zoned way back or have to sit behind your minions if you want to farm. The same principles apply to basically all supports.
Speaking of, regarding champions, play whoever you like and whoever you're willing to practice on, champions you have success with, etc. I would try every support champion at least once or twice, but when it comes down to what you actually play, pick like, 2-3 champions that you like and do well with and just play those. Spreading yourself too thin as far as champion pool basically makes it so you're mediocre at all champions, master of none. Yes, champions have various strengths and weaknesses, but being able to play a champion well will mask those weaknesses. For example, Soraka's main strength is her ability to sustain in lane, but she can dish out some really mean harass with her spells and auto attacks (she's got pretty high base damages and her AA range is the same as most ADCs), especially if you're just relentlessly hammering away on your opponent (moreso because harassing with your Q heals you, enabling you to sustain even better), and her silence can destroy people in fights. Moreover, and this is true with every role, focus on the fundamentals of the game/role. This is easier if you have a champion you really know well, because instead of wrestling with the champion's mechanics, you can control them instinctively and focus more on the game. Finally, some champions you just don't play well, or your playstyle doesn't match their strengths, but that's not an issue, just find what works for you. I think Nami is an amazing champion, if you like playing her, keep at it, but I don't play her because I'm not happy with my bubble accuracy (or lack of) and the cast time on her ult bothers me; on the other hand Janna's one of my favorite/best champions, but if she's not working for you, don't force it; everyone plays the game a little differently.
Speaking of Janna, I always see people touting her as this disengage heavy support with a passive playstyle, etc. etc. which is true to an extent, but I want to stress that none of this is dogma. Most players I see playing Janna play pretty passively, just disengaging with her Q and shielding you from poke every once in a while. I play Janna pretty aggressively; vs opponents who aren't providing much presence in lane I can often single-handedly force both of them to back with just my shield and auto attack harass (vs. more evenly skilled opponents I'm still constantly looking for opportunities to harass and poke and zone). In fact it's probably because Janna is so good at disengaging that I can afford to play as aggressively as I do, because if I overstep my bounds I can easily disengage and reset. (This isn't me telling you to play Janna; again if she's not working for you, she's not working for you. This is just me illustrating Aphromoo's point about providing lane presence; you can easily do the same thing with Nami since she also has an AA buff and sustain, as well as strong CC).
Some more general advice; your goal as a Support is the same as everyone else: you're trying to win the game. Most people think the support is at the mercy of the ADC; it's actually reversed, the ADC is your damage tool to win the game. The reason you're in lane to begin with is just to get some experience/a bit of gold, and basically while you're there, you might as well try and get your team's 'weapon/sustained damage tool' aka the ADC ahead of theirs. As a support you're an enabler, meaning you're the person that opens the door (through your base utility/utility from your items) for your team, they just have to walk through (aka deal the damage, right click on turrets and enemies, etc). It's not that you have no farm and therefore you're weak; it's because you don't have to sit around in a lane/jungle and farm creeps all game that you're useful, you're free to control the map. If your ADC literally cannot last hit to save their life, go gank another lane, get someone else ahead. Your teammates are tools for you to win the game; if one isn't working properly, go help a better one (conversely, if one is doing well, help them do better; peel for your carries, etc). Look for opportunities to ward; enemy jungler just showed top? Go light up their bottom side jungle; it's your jungle now (careful of enemy laners collapsing on you).
Some even more general advice; work on your gameplay fundamentals, which means your mechanics, game knowledge, etc. I learned to play ADC after being frustrated supporting ADCs who couldn't last hit or kite (basically, as support I was giving them a free lane by forcing the enemy back, but the ADC didn't capitalize on it ie. 'didn't walk through the door'), and learning to do both of those helped immensely with me learning to play support more aggressively and really abusing my opponents with auto attacks, as well as just learning general lane dynamics and how an ADC thinks and how to work with that. Also, don't underestimate your own auto attacks; sure one Soraka banana isn't going to hurt too bad, but you chain a bunch of them together, especially if you can kite and stutter step as well as an ADC main, and that damage really sticks (FYI, Soraka and Sona have the same base attack damage as Caitlyn; they're also higher than a number of ADCs like Varus, Twitch, MF, etc. You add an AA steroid like Janna or Nami, who have even higher base AD, have and their autos seriously start to hurt; yes I know the ADC's runes/masteries/doran blade creates a larger gap etc. but I'm just pointing out that you can deal a ton of damage with autos, especially since you're not busy wasting them on last hitting minions). Plus if you're taking the utility mastery, poking the enemy just means more gold for you.
Hope that helps
. At the moment, I'm working on 
to branch out from tank supports and work further on my skill shots. Up next after her is 
.
.
, this 
, obviously this 
and either 2/1 of these 
and 1/0 of these
. Place it in either your tribush, the river bush if against a Shaco or Evelynn, or if your ADC doesn't mind you roaming for an extra 20 seconds behind the red buff bush (if starting blue side) or in the Dot brush in the center of the river. Can also be placed in the bush behind the blue buff. Not sure what to call it exactly.
C:
