If your walls are all the same color, then painting into tight corners does not present much of a problem. But if your walls are different colors, painting a tight corner can be challenging. Follow these steps to achieve clean corners when painting:

1. Paint both walls and stop just short of the corner.
2. Choose the lightest colored wall and paint it completely into the corner, and do not worry about getting paint onto the other wall.
3. Using painter's tape, tape the corner of the wall that you've completely painted (the lightest colored wall), ensuring that the tape is as close to the corner as possible. Use hard pressure when taping to ensure against bleeding.
4. Now paint the corner again with the lightest color, allowing it to bleed. Since it will bleed onto its own color, it doesn't matter that it's bleeding. Allow that paint coat to dry at least three hours, leaving the tape in place.
5. Now that the bleeding process has cured, you can paint the opposite corner with the darker colored paint. Use an angled brush to paint the darker color into the corner, taking care not to paint beyond the painter's tape.
6. Allow the paint to dry overnight, and then carefully remove the tape.

Another method for painting into tight corners is to use an artist's brush in the corner, before painting the rest of the wall. Use a quality artist's brush with angled bristles and paint a strip about one-inch wide from the ceiling to the floor. Take short strokes, using plenty of paint per swipe. Since smaller brushes use less paint, you will need at least two coats of paint per wall. Once you've finished the corner strips, paint the rest of the wall.

One more method of painting into tight corners is the paint-and-wipe method. Quickly paint as much paint as you can straight into the corner, without worrying about getting it onto the other wall, and then just as quickly use a very damp rag to wipe the paint away from the facing wall. If you are using any color but dark red, this is a great method for painting tight corners.

I've also found sponge brushes are great for getting paint into places that a regular paintbrush can't reach, like the small bit of wall between two door jambs. Sponge brushes are actually bits of sponge, glued to a wooden handle. Manufactured to be used and then thrown away, sponge brushes are inexpensive and easy to use. Just make sure that you have enough paint in the sponge, since they are highly absorbent.