I take the neck off of all my bolt-on instruments and inspect the neck pocket.
If there is any stray glue, rubbing compound, paint or any other foreign material in there (or on the neck), I sand it off to ensure a solid wood-to-wood contact point. Then I put the neck back on, tightening the mounting screws as tight as possible without stripping the threads.
IMO, solid wood-to-wood contact is critical for improved tone and sustain for instruments with bolt-on necks and this is an easy way to accomplish that.