First, you should find a champion pool you enjoy the most, usually consists of 3-5 champions. This will entirely depend on your play style. Practice and try to master these champions. Once you feel confident with them you can be saying "Mid Pref, Jungle Pref, etc."
Second, Try to be able to play every role. You don't have to be the best at each, just be sure to know the basics and how to fulfill your job as that role. This includes understanding how the champion you're using works.
Third, watch or read guides online for basic concepts such as runes/masteries and mechanics. Once you understand the champions you will be using, this should come at ease since you understand what makes them strong and what is useless.
These are just basic tips, but they can go a long way in the aspect of gameplay. (You have to get the basics down if you expect to be good)
I can give you advanced tips as you improve. I may only be in silver but we are in the same boat. It takes time and effort to improve, in time you'll be better.
~ Riataro