[pushkins]

Wipe it down with a damp sponge, make sure you keep the sponge clean by rinsing it out very regulary. You then could either spray the ceiling but you'd have to rent or buy the spray unit. If it were me I'd use a good quality roller and a good primer and roll the primer on the ceiling.
If you want an even better finish you could prime the ceiling with Zinnzer (gold label) but be prepared, it is oil based and cleaning up is a chore.

Make sure you use drop cloths or either way you'll be cleaning up for a long time.