well that's tough cause that's about everything lol. tutorials aside (but they are VITAL to improving), study your favorite artists' work as they progressed from beginner to advanced manips. watch what they changed and how. i don't have time to write a book, but i will help as best i can. let's see.. question, when you work on your manip, do you work on it at full stock size? and then resize down at the end? i can give you some tips to smooth/blend/finish off a piece nicely.