The way you integrate the backstory often makes or breaks your writing.
Stephen King recommends getting to the backstory as early as possible, and I mostly agree with that.
If there’s something important about your protagonist’s backstory that will play a role in the narrative, don’t introduce that information on page 312.
Don’t introduce it on page 2 necessarily either, but do introduce it early on. Have the reader thinking about that piece of the character’s backstory, even it’s just at the back of his or her mind. Doing so will allow the big moment that happens later to have a satisfying payoff.