Much debate has been used on the use of flashbacks.
Flashbacks, for the most part, are seen as amateurish, the mark of a beginning writer trying to be clever in his/her storytelling.
But can it be of use?
The short answer is yes. Flashbacks, in one form or another, is seen in most books. Even the mere mention of something in the past could be considered a flashback of sorts--okay, many will think of a flashback as the world around you growing wobbly, swirling, twirling, transforming from the now to the world of then. Mostly, it's used to establish a past of something. Could we really read about Harry Potter, knowing he's an orphan, and not wonder what happened to his parents? Rowling is a genius, though, for not delving too much into Harry's past. She establishes that they're dead, it was tragic, and moves on.
If a flashback is really needed to tell about one's past, try this method: tell the story at the beginning, chronologically, and then we'll see it for ourselves. If that doesn't work, insert slices of it throughout your book to pull the reader along.