Writers, especially beginning writers, often find themselves wanting to blurt out everything up front. This often shows up as a flashback early on in the story to show the back story or event that first sent the protagonist off kilter.
Keep in mind throughout to pace the info you share with the reader. In each scene, only put in as much as is needed to inform that particular scene (this can include foreshadowing clues of what is to come, but don't overload the scenes.) Invite the reader in slowly, but with a bang. Keep curiosity high = creates a page-turner book!
Don't tease the reader, but don't give them everything. Allude to problems, tension, conflict, who the character truly is, but hold back from revealing the details. Curiosity is one of the most powerful ways to pull the reader deeper into the story.
Hold off with flashback and even memories, if you can get away with doing so, until the Middle (1/2).
Also, be careful how many characters you introduce at a time. Introduce slowly and keep names to a minimum -- make sure we meet the protagonist first and get a clear idea who she is and that this is her story before moving on to the secondary characters.