Lately I've been working with a few lovely and talented beta readers and I notice they grapple with a common issue. Back story overload. Once I cut away two thirds of what they had written (and my their writing was lovely!) the wonderful stories they were telling emerged, glistening and lovely as morning dew. And, to their credit, each of them accepted the bloodbath and rewrote, to excellent results. I've been calling this bloodbath, "Killing Your Darlings" for years, a phrase I have gleefully borrowed from Stephen King from his book, ON WRITING. (If you haven't read it, get it NOW.) http://www.amazon.com/On-Writing-Stephen-King/dp/0743455967
I also find that backstory, how little or how much to include, still gives me headaches at the beginning of any new WIP. When I noticed this excellent blog post about back story dos and dont's I had to share it (with Janice Hardy's generous permission). You really should check this out. I think I'm going to look at this website every day. It's a huge treasure trove of writerly information.