Barbara, what kind of ceiling do you have, flat or popcorn. If flat, wash with Dirtex, apply a primer/sealer and then paint. If you have a popcorn ceiling, use the search feature here to look for some of the posts by Mr. Paint on this subject. He posted on this subject several times with some details that appeared to be really helpful for this.
The most important instruction for either type is to fix the source of the water so you do not get water spots on your ceiling again.