Often you are going to hear high-level players saying that support is an elo inflated role. And yet, do you still have a problem with climbing with it? Here are some tips to make that a bit easier.
Supports, true supports, in League of Legends can be broadly classified into two categories. These are the enchanters, and engage supports. Of these, the engage supports are your best bet for climbing low elo.
While enchanter supports, usually, offer more to the team, that is based on the fact that you can trust your team to play well, and that is never a good thing. Enchanters, as a rule, rely on playing passively, rather than making the plays themselves, as well.
Now, you must be wondering, what does one do when playing as Leona, and their ADC just isn't following through on their engages. In that case, roaming is your best friend. Find another carry to feed them kills, whether they are your midlaner or our jungle, and playa round them. Be advised, though, that the problem may not be in your ADCs though, but the fact that your engages are, perhaps, not optimal.
And that brings us to our next point, which is learning match-ups. Consistency is what differentiates the good players from the bad ones, and learning match-ups is the way to do it. To help this along, and see the result quicker, limit your champion pool to two, maximally three champions, for the best effect.
Though you are a support, you must also know the basics of wave management. Help your ADC push and freeze when needed, ping them into oblivion if they themselves don't know in what position the wave needs to be before backing, or just shove the wave yourself if it has come to that.
And last, but definitely not the least, is warding. Your teammates can't be caught out, no matter their missing map awareness if you have all the strategic bushes warded, especially in advance for objectives such as drakes or barons.