You can paint over plaster, but repair any damage to the plaster first, or the paint will crack and bubble. You should also prepare the surface of the plaster to accept paint, which gives your paint job the best chance of looking good and lasting a long time. Before applying the color you want, apply a coat or two of primer. Additionally, use latex paint, and choose a latex paint with a satin finish for areas with dampness, like bathrooms.

Wet-sanding and dry-sanding each have pros and cons. Dry-sanding is less messy, so it’s a good option if you’re trying to minimize dust (for example, if you’re sanding an occupied home or working with particularly dry or dusty drywall mud). However, dry-sanding is quicker because you don’t have to keep rinsing a sponge or wait for it to dry before painting.

A common cause of separation between a wall and the ceiling is truss lift—this can happen to the ceiling of rooms directly under the attic when the seasons change and wood building materials dry out, shrink, and shift. Roof trusses often dry out at different speeds, and if the bottom pieces dry out faster than the top pieces, they can shrink and pull the attached drywall away from ceilings and walls, causing cracks. Fortunately, truss lift is only a cosmetic problem, not a structural problem, and you can fix it by separating the ceiling drywall from the roof trusses, and patching the cracks.

You should always hang drywall from the top down. Starting at the top makes it easier to create a straight, tight line between the ceiling and the wall. Any gaps that occur will be at the bottom, where they are easier to manage. You can either cut the bottom piece of drywall to fit the remaining space or cover the gap with baseboard trim. Additionally, starting at the top is physically easier, as you won't have to fit the top sheet into a tight space between the lower sheet and the ceiling, or try to balance the upper sheets on the lower ones while securing them.