It was here that I ran into the same problem I did in Season 3. I could not get any higher. I would get to around 90 LP and then suffer a string of defeats that knocked me back down to 0 LP. This process repeated itself for several weeks and was quite infuriating.
I eventually realized I had hit a plateau with regards to my skill in the game. What clued me in was my massive losing streak with Leona. At one point I had a whopping 80% win record (over 20+ games) with Leona but then lost a bunch of games in a row. When I started to play Thresh I started winning again and I attribute that to learning new skills that helped me move on from my plateau.
While some skills are universal, like map awareness, where to place wards and wave control, there are some skills that are specific to champions. For example with Thresh I had to learn to better predict champion movement because of the short delay with his hook.
Learning to play Thresh also improved some of those universal skills. A good example is map awareness. With Thresh's lantern, having good map awareness is even more important for setting up ganks or saving team mates. With Leona, map awareness was mostly useful for avoiding ganks, so I did not really pay attention to the position of my team mates. After playing with Thresh for a while I've become much more aware of my team mates (especially my jungler) and I've pulled off a few lantern ganks and lantern saves that have swung fights in my team's favour.
With that said, I made it into Silver 2 earlier this week and I'm hoping my skills have progressed enough to get me further. Going for Gold by the end of this season!