A problem I often find in the plot consultations I provide to writers is the misuse of flashbacks.
During a plot consultation, a writer outlines her historical novel to me. Before long, the story takes a u-turn into flashback. My immediate reaction is to refocus myself. I quickly scan the Plot Planner I am creating for her for what I know of the story so far ~ the time frame, the place, and the characters ~ in order to keep in perspective the time and place change.
If you've read Blockbuster Plots Pure & Simple, you know I am not a fan of flashback. Mostly, I dislike the whiplash effect, but also because I have seen too many writers, especially writers just starting out, overuse and abuse flashback. It is more difficult and takes more thought and creativity to integrate the pertinent backstory seamlessly into the front-story than it is to create a flashback. Flashback is a depiction of a past, literal experience. Full integration of back-story into front-story involves more nuance and skill.
Three plot tips when it comes to flashbacks:
1) If you feel you just have to have a flashback, wait to use it in the Middle of the story. By then, the reader has had time to ground themselves in the front-story and is better able to transition back and forth in time
2) A flashback is portrayed moment-by-moment in scene. Consider instead using a memory (summary)
3) If flashbacks are integral to the overall plot and structure, do like Audrey Niffenegger in The Time Traveler's Wife, make the story line non-linear and create the very structure of your story based on time jumps.