Some solid tips for painting a room are to make good use of rollers for open walls, to use a special tool to get edging straight, and to tape off baseboards and moldings to ensure that colors don't bleed into one another. Good preparation is the key to a solid paint job.
Before opening a can of paint, it is important to move or cover all furniture, rugs and carpets. Then use painter's tape to block off baseboards and moldings.
Make sure that all paint is mixed well by having the colors put in the machine at the store or using a drill attachment. Then, paint the edges of the first wall with an edging tool. There are many such tools available, but the type that looks like a thin sponge on a handle works well, providing nice, straight lines.
Before the paint from the edging dries, roll paint onto the rest of the wall. Allow the entire wall to dry, and then evaluate whether it needs a second coat. For moldings and baseboards, use a brush with a short handle held horizontally so that the brush surface is parallel to the floor or ceiling for more control.
If a paint job takes more than a day, clean up properly at the end of each session. Put lids back on paint cans, and clean brushes or rollers for reusing later. If there is no time to clean them, wrap each in a plastic bag to keep them moist overnight.
Allow the paint to dry for 24 hours, and then remove the tape. Do not allow the tape to stay on for long periods because it can become difficult to remove.