If you're a seat of the pants writer like me, you may find that you end up with a lot of backstory in your initial drafts. My advice is to cut, cut, cut as you edit your manuscript, but keep all that informative information in the back of your mind or even better, in a character profile document, to help you understand your characters better. Knowing their backstory will help you create multi-dimensional and realistic characters, but your readership will only need to know the smallest portion of that backstory to understand and believe the current story being told.
Keep cutting that backstory until it's down to bare bones, take a break from it, and then read it over again. You can always add back in another detail or two if need be, but you'll never know if the story could have done without it if you don't strip it out to begin with.