I never liked anything I did, either. I had to learn (the hard way) that your imagination is limited by your knowledge. You may feel like you have awesome ideas (and you probably do!) but they will always be filtered through your fundamental skills. If those skills are lacking, the image produced by your imagination gets watered down and ultimately does not reach the potential you'd envisioned. So: to overcome that, I just practiced my fundamentals in the life drawing room. I drew countless thousands of gestures, studied how to build on that with basic forms, and then how to distill all of that into simple, readable graphic shapes. The figure is helpful for this because it's a very complex thing, which means that learning it will make other things easier. From there I continued doing my own imagination art. Inevitably they'd still fail, BUT I was starting to see small improvements. That buoyed my spirits and I was just always very honest about where something failed, and then sought out exercises to shore up those deficiencies. In a few years I was able to create something that I could be happy with. I hope that helps!