How I fell from Silver IV to Bronze IV, and then climbed back up to Silver III.

In S4 I got lucky and placed in Silver IV, but then fell to Bronze, and leveled out around Bronze II or III. Then In S5, I bombed my promos and got placed in Bronze IV. Oddly, this was kind of a blessing... Since I was already at the bottom of ranked, I no longer had any fear of falling divisions, and started playing nothing but ranked games. In a few months I climbed 6 divisions and I'm currently in Silver III.

I think one of the best things you can do to improve in ranked is to play more ranked. Don't worry about falling down the ladder. You're only going to fall as low as your skill level is. If you fall to Bronze 2 and level out there, that means you're current skill is Bronze 2, and that's fine. In fact, that's where you're going to learn the most. You're other option is to stop playing ranked, and try to improve in Normal games, but this is a mistake because you learn so much more by playing ranked games. Any time you play a Normal game you are wasting your time. Even if you fall several divisions initially by playing only ranked games, you will climb back up to where you were faster than it would take you to increase your skill to that level by playing Normals.

On top of that, being where your actual skill level is on the ladder allows you to accurately gauge your skill level, monitor your progress, and see the results of your improvement. Improving, winning, and climbing feels good. It feels a lot better than desperately trying to hold on to a division you're not really good enough for.

Bottom line: my advice for ranked is to play nothing but ranked games. Though you may fall initially, you'll learn faster, and climb back up higher than the division you are currently struggling to hold on to.