There are a lot of really great books out there on writing, and there are many that I could recommend, but one of my all-time favorites is How Not to Write a Novel by Howard Mittelmark and Sandra Newman.
This is a great little book. As the authors state, it is hard to tell you how to write well, but sharing observations from many years in the publishing industry--that they can do. And boy, do they. "200 Classic Mistakes and How to Avoid Them--a Misstep-by-Misstep Guide" is the book's subtitle. Not only do the authors give valuable examples of things that will make your prospective editor wince, they are also roaringly funny. Particularly if you like tongue-in-cheek humor, as I do.
I'm currently re-reading it, both because I was in the mood for something funny and also because I wanted a refresher course. Several times as I read it recently I said to myself, "Ah-ha, I recall that I was about to do that, or started to do this, and then I fixed it." That sort of impartial self-quiz is very useful, particularly when you don't have a regular critique group. It also makes me proud to remember when I used to make such mistakes in my writing, because it shows me how far I've come and how much I've learned. I love it when I can say, "I'd never do that now."
You can also check out their website, www.hownottowriteanovel.com, for updates, articles, and further hilarity.