Or if you are not sure what paint was used last. I always use a primer when in doubt .

If you are painting bright colors pre tinted primer will help cover the new color. If the current wall is already sealed well, then just paint two coats of paint over it.

Good luck:)

Prep work is key if there has been structural work, but is also key to any good paint result.. A primer will not cover nail holes, or drywall damage. For that, you need drywall skim coat, at the very least a good spackle to repair dings and nail holes. Consult your paint store, and they can advise you. Or.........pay a pro painter! If you are a renter, and simply want a new color, and the bed will be in front of the less than perfect area...............and you don't require perfection.....have at it with the roller!!

These walls need a good cleaning as well. There are some darker areas that look suspiciously like a dirt/oil line. If that dirt isn't taken care of, then the new coat of paint won't stick. Clean it and do a light sanding before deciding on primer+paint vs. paint