Cutting In
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.
To texture into corners and next to trim, use a dry roller with the sleeve pulled off of the roller cage about an inch. The sleeve will then clear the end of the cage, and the roller can reach almost to the edge of the wall, giving more even coverage.
If the trick with the roller sleeve did not take the texture far enough into the corner to suit you, you can use one of the special rollers made for inside corners. They look like soft pizza cutters - foam wheels with V-shaped rims.