Allow your first coat of paint to dry for a minimum of two hours. Fans can expedite the drying process, but if your space is dusty, the fan may cause dust particles to stick to your paint, so an open window is often a better choice. Test the paint dryness before you begin your second coat; touch the paint with one finger -- if the paint is still tacky, it is not ready for your next coat.
Restir the paint in your can thoroughly using a wooden stirring stick, often free from the paint department at a hardware store. Pour the paint into a paint tray.
Paint the perimeter of the space first with a small roller, or a brush if you are working in corners. Carefully roll or brush approximately 3 inches along the perimeter, using even, smooth strokes. Get as close to the very edge of the space as possible, meeting the painters tape when applicable. After you run a brush vertically down a corner, use a small roller to smooth out as many brush strokes as you can.
Dip a 2- to 2 1/2-inch wide roller into the paint tray and roll out excess paint on the tray's raised lines. Start applying paint along the top edge of your space. Work in small sections when you are painting a wall; Behr recommends dividing the wall into 3-by-3-foot sections. Work the roller in a "W" formation, overlapping each "W" you make until the section is completely covered.
Stand back and make sure that nothing of the first coat of paint is showing through. Typically, your paint will dry slightly darker than it was when wet, so the dry first coat will be visible even though it is from the same paint can as the second coat. Reapply paint as needed to cover the first coat.
Move on to the next small section, repeating the "W" formation technique. Blend the edges of each section together to reduce paint lines once the second coat dries.