Tru Oil is a varnish. For removing dust nibs, etc, I like 400 or 600 grit sandpaper, and prefer the 400 as it doesn't corn up as much. Since you have stained your grips, 600 grit is probably a better choice so you won't cut through the Tru Oil and sand your stain. You don't need to sand the entire surface, though doing so may make for a better mechanical bond between coats. I'm doing two stocks now with Minwax Tung Oil Finish. Filling the pores is very slow, but must be done if you're going to "finish the finish". I'll use grain filler in the future. Get Flexner's book, it's all in there.
