In the past, I had tried taping the edge. This didn't work out so well. The walls and ceiling are textured, so paint just seeped under the edge of the tape. I had to redo the entire edge. Taping that way was worthless.
Doing it completely by hand, as recommended by some, took me even longer.
So, I turned to the internet for advice. This article was particularly useful. http://lifehacker.com/5975243/whats-the-best-way-to-paint-edges
I decided to try the trick described by commenter "esac," about halfway down the page.
Step 1: Paint the ceiling. Pay no attention to the edge. (Very easy.)
Step 2: Tape the ceiling.
Step 3: Paint the wall-side edge of the tape with the ceiling paint. This way, any paint that seeps under the tape is the correct color for the ceiling. This seals the edge of the tape from any more paint flowing underneath.
Step 4: Paint the edge of the wall with the wall color. (Still easy.)
Step 5: Remove the tape.
I forgot to take after pictures, so I will describe the result with words.
It was not perfect:
- There were a handful of places where the tape caused the wall paint to peel off. These areas had to be touched up with wall paint. It seemed to work better if the tape was removed immediately after painting, before the wall paint had any chance to dry.
- There were a couple places where the wall paint still made its way underneath the tape. But it was minimal. These areas had to be touched up with ceiling paint.
- There were a few places where the tape pulled the texture off of the ceiling. These areas had to be touched up with ceiling paint.
Overall, the process worked pretty well. The next attempt will be to use better tape to avoid pulling off the texture, and to remove the tape immediately after painting each section.