Years ago, you have a book you had written. It's okay. But you know you can make it better, so you set out to work on it. In order to do so though, the books needs changing. A lot!
This is exactly what I'm going through right now as I write the sequel to Beholder's Eye. It's a story that, honestly, I started nine years ago--December 2004, to be exact. I had a prologue, the first three chapters complete, and the beginning of the fourth.
I kept the prologue--after a heavy revision--and I have thrown the rest of it away. Well, not completely. There are a few bits here and there I'm keeping, but by and large I'm starting over from scratch. And it's turning out much, much, much, much better than before.
Whenever you're in a situation where you're doing a lot of heavy revision on something you wrote years ago, try this: write it over, completely from scratch. See how much better it turns out.
This isn't the first time lately I've been doing this. I have a novel I wrote before Beholder's Eye (my fourth completed novel) that is going through major changes as well--I've stopped working on it so I can continue in the Central Division Series, with Beholder's Eye as book one.
(Beholder's Eye will be published shortly, as soon as I can get a cover completed. I'm getting the money squared away and I'm crossing my fingers that this week I'll make it happen.)