In all my recent years writing novels, I don't think I've ever written a flashback. I don't think I've even considered writing one. The thought just never crosses my mind.
Now, as you've hopefully come to expect from me, I'm not going to say, "Never use flashbacks!" I have no doubt that, in some stories, they work very well. However, you should be careful about using them because they do have some flaws.
Flashbacks don't advance the action. This is quite literally true, because flashbacks by their nature have already happened. No matter how interesting or action-packed a flashback is, it's not going to be as relevant as what's happening in the present, because there is no real choice happening. The destination is pre-determined.
Flashbacks don't surprise you as much. When you read a flashback or watch a film flashback, do you feel the stakes are as high as when the characters are actively doing something in the main tense of the movie? Probably not, because you know certain things can't happen in the flashback. Certain character developments can't occur because you know the present situation, for instance. Certain characters can't die, for instance. Sure, flashbacks can be surprising, but by their nature they will never be as surprising as what happens next.
You will always know some things can't happen in a flashback, whereas you can never be totally sure of what will happen in the present moment.
I've often brought up the word:idea ratio, that whatever you write and include should accomplish a lot of things. For me, I never use flashbacks because I'd rather have characters present the event in the present, which both establishes the needed details of the past while also advancing the relevant present-day drama, which of course can snake in any direction under the sun.
For example, if a character discusses a harrowing episode with a friend, we not only get the details of that episode (which might be important in explaining why she is the way she is today), but we also get her perspective on it right now. She might get angry about it, or stop talking about it. She might want revenge or want to forget it. She can make a choice about what to do next.
And if a conversation feels too dry for the material, then make a character compulsively paint about it, make a character mirror it in a play or at work, make a character do something wild because of what happened... You can spice up the present events to elevate the drama, if action is what you need.
No matter how you look at it, you can accomplish more in less time by not using flashbacks.
Some might say that we can't really feel our "harrowing episode" if it isn't set up and recreated in a flashback. There's some merit to this, because of course a well-written scene will capture that episode vividly. However, I would thus challenge our imaginary interlocutor: In a really, really well-written scene, could you not capture the present action, dialogue, feelings, and choices as well as the important, shocking details of the past?
Of course it's possible. Now, would a flashback be easier than accomplishing all of that at once? Yes, but it's not about what's easy. In a previous seminar we discussed the perfect story and how hard it is to make. Foregoing a flashback to create a vivid, emotionally engaging scene in the present can be tough, but it is usually the better scene.
So, if you find yourselves writing flashbacks, think carefully about them. Think, is this really the most engaging way to present this information? Think about how you feel when you read or watch flashbacks. Do they feel like info dumps sometimes? Do they feel like they insult your intelligence sometimes, like you don't remember what happened? Do they feel a little dry because you know a lot of what happens next?
Occasionally, writers frame the entire story as a flashback. They start with the ending or some midpoint, then flash back to the beginning and go from there. It works a lot of the time, but be very careful. I have often heard people express a disconnect with such stories, saying, "I already know such and such will happen, so the drama just isn't there for me," whereas I have never heard someone say of a story that is not a flashback, "I don't know such and such will happen, so the drama just isn't there for me."
Not knowing the future is what makes that next step so interesting. Supply more of that, and less of what the reader already knows!