Bronze to Platinum

Season 3 I started out Silver 3. Every season after that I rose to platinum. Now, in season 8, I am Platinum 1.
Here's what I will suggest.
Try to find your 'go-to' champion. Find a champion that you personally love and are good with mechanically (mechanics are a whole nother topic). Then, you can start working on learning the game itself. Learn specifically about what champion counters what.

Learn about map control and vision (as a jungler main, this is extremely important). My stats say that I have 60% map control in games compared to 43% of diamond players playing the same champion. This one is huge and it definitely makes a difference when you can control dragon, baron, scuttle, vision, etc. However, depending on your role you may not have too much control on this.

Lastly, one other thing that helped me is to watch other players. See what they build in different circumstances. What path they took. Why they flashed there and did this-- etc.

Good luck!