This story covers the basics for painting walls.
Painting a wall shouldn't tire you as quickly as painting a ceiling because you're working more at shoulder level (if you stand on a platform) or just slightly above, with a roller and extension handle.
The procedure for painting walls follows the same general principles as painting a ceiling -- cutting in the edges with a brush, then filling in the balance with a roller.
Because the surface texture of brushed paint looks different than rolled paint, try to get the roller as close to the edge as possible to minimize what will be a noticeable difference.
Painting a wall (or ceiling for that matter) is a task made to order for two people, one with a brush, cutting in the corners in sections, and the other following with a roller and filling in. That way, tandem painters will eliminate any lap marks caused by applying rolled paint to an edge that's already dried.
A brush is the common tool for cutting in, but you may find using a paint pad easier. Paint pads leave a thicker coat of paint, so be careful the paint is not overly thick as it comes off the edge of the pad.
From 4 to 8 hours for a 10x12-foot room, depending on your experience and skill
Brushes, rollers, extension handle, ladder, paint buckets
Using brushes and rollers
Prep and prime surface as necessary
If you're painting the wall the same color as the ceiling, you don't need to mask off the ceiling. Different colors on the two surfaces, however, require you to mask the edge of the ceiling with 2-inch painter's tape. Make sure the ceiling paint is completely cured before masking it. Otherwise you risk pulling the ceiling paint off if it's too fresh. Starting in a corner (usually, but not always along the bottom of the wall) and using a 3-inch brush, cut in a band of paint about 2 inches wide, extending it 3 to 4 feet horizontally and vertically.
Once you've filled in the area, finish it with light vertical strokes to smooth the paint and remove roller marks. Alternate between cutting in and rolling until you've completed a wall. Don't take breaks or start a new can in the middle of a wall -- you'll create a noticeable lap mark.