Personally I prefer a story that starts somewhere in the middle of the action and barrels down the track, to the photo finish end, in a nice zig-zaging, uphill, forwardly moving procession.
Be frugal with flashbacks and back-story.
If you're using a lot of flash backs in your story, consider that you may actually have two independent stories. Maybe the story you are trying to write needs a prequel instead of a lot of back-story in the current work. Try pulling all your flashbacks out and see if you can tell the current story without them.
If you can leave something out and still tell a coherent story, then you didn't need it in the story in the first place.
However I'll admit that flashbacks can enhance some stories.
Before using a flashback please research the good, the bad, and the nightmarish.
There are a lot of good examples and references out there. Please read several.
Here's a good place to start: