As a reader, I HATE prologues. The few that I've liked have been the "Once Upon a Time" style openings where you NEED to know that the Beast had until the last petal fell or else he'd die. That kind of thing is important.
A problem that I've see a lot of writers do is oversaturate the "prologue", they'll introduce characters, drop you into the middle of tense scenes, etc all without any build up. These types can go on for multiple characters. When we finally get to the "first" chapter, it feels disjointed and disorganized so I put it down.
If the scenes are important, I like using dreams and conversation to show it to the readers. For example, camp fire stories. One character could be narrating what happened in the flashback to other characters.