This piece by Giles is a spot-on description of what I do in my role as content buddy at Clearleft. Especially this bit:
Your editor will explain why things need changing
As a writer, it’s really helpful to understand the why of each edit. It’s easier to re-write if you know precisely what the problem is. And often, it’s less bruising to the ego. It’s not that you’re a bad writer, but just that one particular thing could be expressed more simply, or more clearly, than your first effort.