If you want to improve your writing or produce the best work you’re capable of, and you have your choice of editors, look for one who will tell you the truth — even when she thinks you won’t be happy to hear it.
When you hand a draft to someone else to read, tell that person what you need, and be honest. If you say, “Be critical,” listen with an open mind when they are. If you say, “My ego needs a boost, so be nice,” they should hear that message and respect it as well, though it probably won’t improve your writing.
Be clear about the level of editing needed. If your work requires conceptual development to reach its audience, the right editor should be able to give useful feedback. The editor who copyedits or rewrites instead of helping you develop your concept to reach your audience is not the right editor for the task.
The most important thing is to choose an editor you trust. Do it for the sake of your writing.