Strip the wood. Move the table outdoors and apply a chemical wood stripper. This will remove the finish down to the bare wood. If you prefer a nonchemical approach, a heat gun can also be used to help remove the old clear coat on the table.
Sand the finish off of the table. Use a heavy grit sandpaper and go over the entire table, removing the remainder of the finish and the former wood stain. Keep going until the entire table looks like fresh wood.
Gouge the table. Rustic furniture typically has dents, dings and gouges missing out of it. Fill a cloth bag with nuts and bolts and hit the table several times in a random pattern. Keep going until you are pleased with the amount of distressing on the wood. Remember to wear safety goggles during this procedure.
Stain the wood. You can opt for a regular wood finish or stain the table to your liking. Many "rustic" furniture pieces feature a light hickory or maple stain. This gives the wood some color, without hiding the distressing you just did.
Seal the wood. Even though the table may look old, you don't want it aging before its time. Apply at least two coats of clear polyurethane to the entire table. Sand between coats. This will help protect the areas you distressed so that moisture or dryness does not lead to excessive cracking or mold buildup in these areas.