I don't want to be a downer on you or anything, I was a Thresh main for a majority of season 4 in gold, however i found myself constantly going up and down on the ladder. For a support to climb consistently in low elo at least, in my experience, requires 1 of 2 things, both if possible.
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As a support you need to know every match up, what is strong against your lane and what is weak, as a Thresh main i knew what match ups were in my favor and which were not. Additionally you need to be able to hit a large percentage of your skill shots. You role is literally designed to babysit another player for 15 minutes. You are supposed to keep him alive and get him to a state where he can carry, you carry early he carries late. There is a massive difference between supports who can land 60-90% of their skill shots and those who land 30-50%.
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Find a reliable duo, this may seem trivial and you have probably seen it before, but its the most helpful and reliable way to climb. Lots of low elo adcs are inconsistent, if you find a duo who is somewhat consistent or you have good synergy with, its going to pave the road to Plat.
However i did not reach Plat playing support alone, i turned to the other roles, which had more damage in order to climb, that's where i found my success. Thing about low elo supports, those in Gold/ Silver/ Bronze, is that you could be the best support in your Tier or even the best in your Division. Problem is you as a support are relying on another low elo player to carry you. That is setting yourself up for failure, the best way to climb out of bronze as a support main is to not be one.
Now you may be asking "Erasmos, is there any hope for me to escape if I really have a passion for supporting?" That question is interesting, I want League and E-Sports to grow, and for them to do so people have to enjoy the game itself. People don't enjoy losing or being low elo, or being looked down upon by the higher elos. So if you really want to climb as a support in Gold/Silver/Bronze then you will have to work hard in every game. I've played games in low Bronze on smurf account where i got stuck with support. I knew that the game would be more difficult since i couldn't hard carry the game, however the few games i did get support I won.
Now you may be thinking "Well you're Plat and they are Bronze so of course you easily won," Yes, this is true, I do have more experience in a higher skill setting however, that does not mean it's impossible for you to win with support. I played support Janna all 3 games and died only once every game. I never made any flashy plays that distinguished me as a "good" player. I focused on keeping my carries alive with peel, and not dying. That's the supports job, not trying to make a montage of flash tornadoes or monsoons.
Support is a fun rewarding role when played right, you can be the difference between winning or losing a game with 1 hook, shield, lantern, wall 
, or mass zhonya.
If you have any further questions about league in general feel free to add me: Erasmos.
That is an open invite to anyone who wishes to improve their play. 
i went from Bronze to Gold 1.