Ensure that the lumber is completely dry before proceeding. You can run a blow dryer up and down a piece of lumber -- this is one method -- but the better way is to leave the lumber in a cool, dry place for three days.
Wipe the two pieces of lumber you wish to join together with a tack cloth. Then, in a well-ventilated area, remove any surface oil from the lumber with a solvent, such as acetone, denatured alcohol or mineral spirits.
Sand the two pieces of lumber to roughen the surface and expedite the cohesion powers of the wood glue. Begin with a fine-grit sandpaper, then move to a medium-grit until the lumber feels a bit rough to the touch. Wipe the lumber with a rag.
Reach for a non-water-based glue that is specially made for wood, or an epoxy. Spread your glue of choice on the lumber and clamp the lumber pieces together.
Remove excess glue based on your personal preference: Either wipe it away with a rag while it's still wet or scrape it away once it has dried. Experienced woodworkers debate the wisdom of both procedures, but either will work.