Fewer flashbacks. Most Young Adult novels tend to be shorter and have fewer flashbacks, concentrating instead mostly on the front story.
There tends to be the view by many that if you stick closely with the front story and don't spend a lot of time in flashback that you're writing something "simplistic." Yet, at the same time, lots of flashbacks don't advance the story and cause readers to either skim, or just put the book down, never to pick it back up again.
The more I write and the more I read, the less patience I have for flashbacks. It's not always true, sometimes I'll read every single one and love it. But often I just skim through the flashback to get to the next scene so I can get back to the front story.
In the novels that I've skimmed in this way, I've never gotten to the end and thought: "Damn, this climactic scene makes no sense...I should have read that flashback."
Since I don't say this, I can only assume that many times a flashback, while interesting to those who want the backstory, tends to slow down the front story. We're told constantly as writers, "Show, don't tell." But sometimes I think that advice can be taken to an extreme.
For example...there are things you REALLY want to tell. If a character goes through the normal routine of getting ready and then goes and catches a cab and sits in the cab for twenty minutes, we don't need to be shown all that. The realism of a cab ride just isn't all that exciting. If I see all that I'm already at the skim point.
Back to flashbacks...
Many times, if a flashback doesn't advance a story, it's a case of it would have been better to just "tell it" All stories have exposition, stuff you're just telling. It's the job of the writer to know which parts are better to show and which are better to tell.
If you show something in a flashback, be VERY sure it's advancing the plot and not just advancing your need to show how much of your characters backstory you know as the writer. i.e. don't do it just to be clever.
I've got a few flashback scenes in the novel I'm revising now and I try to keep them really really short so I can get back to the front story. Sometimes you have to have flashbacks and if worked properly they can be great. Just don't write a flashback that all but the most fastidious readers will skim. And don't give people an excuse to put down your story.