You’ll want to know the condition of your ceiling before you prime or paint it. Any damages need repairing or it’ll get in the way or get worse. This is especially true for water damage.
If the paint is oil-based you can paint over top of it with any kind of paint. If it’s acrylic (latex or water-based) then you can’t paint oil over it or it’ll chip and peel quickly.
You can learn the steps for preparing a room for painting. It involves moving objects, covering them, and painter’s tape.
Now comes the priming part. You only need to prime your ceiling if it’s bare drywall or wood, stained or repaired, a high-gloss finish, or an extreme color change.
As for painting, here’s where it gets a little complex. Paint in 4-foot by 4-foot sections starting in a corner. Using your brush, start painting a few inches out from the edge and paint inwards towards the tape. This is called cutting in. It’s like creating a border for you to paint in.
Then, use your roller to paint that section. Roll one way first in straight lines, covering an entire section. Then roll the opposite direction.
Quick transitions from brush to roller help prevent lap marks. Roll a little slow so the paint won’t splatter.
Finally, use a blank roller and lightly smooth out the paint after you finish a few sections.
You can lessen or avoid roller marks by feathering the edge. This means as you roll the paint on, you lighten the pressure so the paint isn’t as thick.