Painting a room is relatively simple if you have the right tools and know the correct techniques.
After prepping your walls, choose the color of paint you would like to apply and transfer a small amount into a plastic bucket liner. This is a good idea for several reasons. First, you probably don't need the whole gallon -- and if it spills, you'll have a disaster on your hands. Better to spend 85 cents on a plastic bucket than $800 on a new rug.
To start, the first surface you should paint is the ceiling -- then the walls, then the trim.
In the beginning, "cut in" the room by taking a brush and painting the areas that your roller won't be able to reach. Good areas to cut in include wall edges, around light switches, and baseboards.
The proper way to cut in is to leave paint deposits vertically down the wall. Paint toward the edges, not away from them. Use this same technique to get a clean line where the ceiling meets the wall.
The best kinds of roller to use are ones made out of foam because they don't leave lint tracks like nap rollers do; they also are easier to clean. They don't hold a lot of paint, but you don't need a lot, anyway. Paint in blocks, one section at a time. More paint accumulates at the edges of the roller; to avoid getting large vertical paint deposits on the wall, make a W, then go over the W with vertical strokes.
Martha used Martha's Fine Paints in Garden and Comfrey Green from Martha By Mail.