When painting, use a brush (a 4-inch brush is the norm) to paint the top edge of the wall, the corners where two walls meet, and the edges where trim has been applied to the wall. A paint roller cannot get into a corner well, so you'll need the brush to get the paint there.
For a more even look, after cutting in with the brush, go back over the area with a very dry roller. This will change the texture to match the rest of the wall.
