First, consider the finish you want. Flat is most commonly used on walls; however, some people prefer satin or eggshell finishes. Semigloss is primarily used on trim. Shinier paints are ideal for kitchens and bathrooms because they are easy to clean, but they're also more apt to show imperfections on the wall.

With any finish, allow enough time to complete your project; the average room takes about four days, including drying time. 

Flatten a cardboard box and place it under paint containers to give floors an extra layer of protection. Mix paint with a wooden stir stick, then pour some into a smaller plastic vessel, filling about halfway. (Spouts on newer containers make this easier.)

Insert the bristles about 2 inches into the paint, then tap them against the sides of the container to remove excess. This minimizes the risk of drips.

Paint part of a corner or around the trim (don't worry about taping yet) with a 2-inch angled brush. This is called "cutting in." To avoid the marks that appear when paint starts to dry, do only 4-foot sections at a time.

Pour paint into the reservoir of your roller tray. Dip in one edge of the roller, then move it back and forth on the tray bed until it's saturated but not dripping. Paint a 2-foot wide V on the wall, and, without lifting the roller, fill it in with tight vertical strokes -- this will ensure even coverage. Repeat, working top to bottom, until you've completed the wall.

Remove all hardware, then sand and prime the surface. With a 30-inch roller, paint one area of the door, such as an inset panel, then immediately brush over it with a 30inch brush. Continue working in sections until you've finished the body of the door, then do the stiles and rails (the vertical and horizontal framing, respectively).

Let wall paint dry overnight, the tape off the trim with painters' masking tap, as shown. (for proper adhesion, burnish tape with your fingertips as you go.) Apply paint with an angled 2-inch brush.

Use a 1-inch angled brush to paint the muntins and an angled 2-inch brush to do the frame, taking care to fill in your seal.

To clean off paint that has seeped underneath the tape, lubricate a single-edge razor blade with glass cleaner -- this will prevent scratches -- and gently scrape the panes. (Using a razor blade on some new windows will void the warranty; double-check yours to be sure.)

Transfer leftover paint to smaller air-tight plastic containers. (Paint kept in open cans is prone to drying out.) Create labels with the name of the room the color was used in, and keep the paint on hand for touch ups.

Run each brush under lukewarm water, then add a few drops of liquid dish soap and continue rinsing. Dislodge dried bits with a metal brush comb. Wrap brushes in paper towels ( to maintain their shape), and lay flat to dry.