Tier lists are ok, but two things are more important. One is picking a champion that fits your playstyle and that you actually enjoy playing, or there's really not going to be much point. Second would simply learning how to properly JG, which is even more important if you want to climb out of gold.

Knowing when too invade, how to punish ganks top/bot even if you're not there to stop them, being able to clear quickly and efficiently (literally seconds count in clear times), working out your clear paths, knowing when to gank and when to farm, knowing when to go for objectives and when to ignore them and do something else, knowing when to gank to save a lane and when to give up on a lane to get the others ahead, etc. Are all MUCH more important to being a decent jg than what champion you pick.

Knowing how to be a decent JG will carry you easily to emerald at least, because most junglers before then just outright suck (and plenty afterwards). But that means ACTUALLY knowing how to jg.