Basic Guide to Working with Molding

Molding Materials
-- Stain-Grade: Clear lumber suited to translucent finishes that show the grain -- relatively free of knots and other imperfections. Pine, maple, and red oak are the most commonly available wood species.
-- Paint-Grade: Lumber intended to receive an opaque finish, which conceals imperfections. Lesser grades of pine are typically used here, including finger-jointed moldings that consist of multiple short lengths of stock pieced together.
-- Engineered: Compressed fiberboard profiles covered with vinyl or wood veneers or primed to accept paint are readily available. High-density polyurethane profiles feature a smooth primer-coated skin and are stable and lightweight

Cut and Fit
Cut and fit the molding for one section of the room at a time, starting at an outside corner. Most right-handers prefer to work counterclockwise around a room.

Basic Molding Installation
Attach
Attach the molding as you go so you don't confuse placement of the pieces. Drill pilot holes in the molding every 16 inches. Use a hammer and finishing nails to attach the molding to the wall. With the hammer and nail set, lightly countersink the finishing nails. Better yet, use a pneumatic finish nailer, shown, which you can operate with one hand while supporting the molding with the other.

Basic Molding Installation
Caulk
Caulk nail holes, joint gaps, and seams where the molding meets the wall. Fill the holes with caulk and smooth with a putty knife. Squeeze a bead at gaps and seams. Smooth the bead with your finger and wipe away any excess. Let dry, then touch up with paint. Caulk minimizes imperfections, but is for painted molding only.
Tip: Paintable latex caulk is great because you can clean up smears with a rag and water.