Working with a paint roller is even less exacting than working with a brush. Even a novice painter can get the feel of it in just a few minutes.
As with brushes, moisten the roller first with water for latex paint or the appropriate thinner for other types of paint. Roll out the excess moisture on a piece of scrap lumber or kraft paper or even on a paper grocery bag. Don't use newspaper because the roller may pick up the ink. Fill the well of the roller pan about half full, and set the roller into the middle of the well. Lift the roller and roll it down the slope of the pan, stopping just short of the well. Do this two or three times to allow the paint to work into the roller. Then, dip the roller into the well once more, and roll it on the slope until the pile is well saturated. You'll know immediately when you've overloaded the roller. It will drip en route to the wall and have a tendency to slide and smear instead of roll across the surface.
The most effective method of painting with a roller is to paint 2-or 3-square-foot areas at a time. Roll the paint on in a zigzag pattern without lifting the roller from the wall, as if you're painting a large M, W, or backward N. Then, still without lifting the roller, fill in the blanks of the letters with more horizontal or vertical zigzag strokes. Finish the area with light strokes that start in the unpainted area and roll into the paint. At the end of the stroke, raise the roller slowly so it does not leave a mark. Go to the next unpainted area, and repeat the zigzag technique, ending it just below or next to the first painted patch. Finally, smooth the new application, and blend it into the previously finished area.
Professional painters also suggest starting with a roller stroke that moves away from you. On walls, that means the first stroke should be up. If you roll down on the first stroke, the paint may puddle under the roller and run down the wall. In addition, be careful not to run the roller so rapidly across the wall that centrifugal force causes it to spray.