I want to say, that it is very important to have a critique partner or group. That person or persons can put things into perspective that you, as your own worst critic and editor, may not see or catch. Just sitting at Starbuck's and discussing the plot of your book can bring that AHA! moment or the subtlest of changes that help the flow of your prose.
Make sure that you establish ground rules, even if they are unspoken/unwritten. When my critique partner and I met for the first time, we barely knew each other. We each brought something to read, but we also found out a little about each other and what we wanted to get out of the "business" of our meetings. We would not demoralize, humiliate, be hypercritical or mean. We would be honest and supportive, offering suggestions and constructive criticism. I would liken it to a couple who are courting, everything is tentative at first, but as the relationship grows, a more open dialog is established. Pretty soon, you each know how to approach critique with your partner.
I am truly blessed with a critique partner, who is becoming a good friend as well. I also belong to a writing group where learning craft is the focus, but we manage to throw in a little critiquing from time to time, and the people in it are honest and constructive, never destructive. That is key!
So, cheers to Lisa and the Golden Wannabe Writers Group! They are awesome!