Usually it's best if the prologue is separated from the rest of the book in some way, such as point of view, character, time, or place. Look at Brandon's books:
Elantris: The prologue is one page and is omniscient POV. Character introductions are saved for chapter one.
Mistborn 1: Kelsier doing something away from the city, where most of the rest of the action takes place; starts in someone else's POV.
Mistborn 2: There is no prologue. Go read chapter 1 and decide why it's not a prologue.
Mistborn 3: Marsh POV, 2 pages; we don't hear from him again for a long time.
Warbreaker: Vasher POV a while before the rest of the action: We don't get another Vasher POV for a while.
Way of Kings: Prelude is 4500 years earlier, then Szeth prologue is 5 years earlier, then Senn chapter 1 is 8 months before chapter 2. These are really 3 different prologues, but Brandon didn't think he could get away with calling them all prologues.
Some books just don't need prologues. If you can get right into the action, get right into the action. If there is no separation between the prologue and the next chapter, the prologue should probably just be chapter 1.
You don't want to have a prologue that is just a big infodump. Elantris's is about as long as you want for something like that: just one page. And is it actually necessary? It was the first book Brandon published, and he's said he'd do some things differently now. In fact, you could almost say Way of Kings has FOUR prologues: Brandon cheated and stuck the infodumpy one on the back cover, plus a tiny bit on the back flap of the book. On the Elantris hardcover, the prologue is also printed on the back cover. It might actually work better there than at the beginning of the book. Of course, back cover text is usually the domain of marketing and you have to be someone like Brandon to influence what it says.