Remove the barrel and buttplate from the stock. This will give you full and unhindered access to the wood and allow you to work without fear of damaging the other parts.
Put on your mask, gloves and goggles, then spray the finish remover over all the stock's finished surfaces.
Wait the required amount of time in the remover's instructions, then wipe away the finish with the varnish-removing scrub pad.
Scrub out any embedded grease stains on the gunstock with your toothbrush, then wipe the residue away with your scrub pad.
Turn on your hair dryer and focus the heat on any oil stains on the gunstock. The heat will draw the oil to the top of the wood where it can be wiped away clean.
Sand down the stock lightly with fine-grain sandpaper -- or a fine-grain sanding block -- to both remove any trace elements of varnish still remaining and to prepare for the new finish.
Wipe the stock down with a fine-mesh scrub pad to remove any sanding dust and also to burnish the stock in preparation for the finish.
Apply wood-filler putty to any large dings or gouges on the gunstock. A putty knife may be useful here, but fingers will also work in a pinch.
Smooth the putty down so that it is flush with the rest of the stock, then wipe away excess filler and discard.
Apply the new coat of varnish or finish. If you are using a spray-on product, simply spray the finish on according to the directions. if you are using a brush-applied product, paint the finish lightly onto the wood using a high-quality paintbrush.
Wait for the finish to dry.