Lester,  There are many ways to tackle this.  Here's one method that
has worked for me on many projects.  There is a two-part epoxy product
called Elmer's Damaged Wood Repair System.  It's a typical 2-part
clay-like product that you knead until mixed, put in place, and let
harden.  I really like this product.  I have filled many stripped and
oversized screw holes with this.

Work the stuff down into the holes with something like a drift pin of
proper diameter.  Really cram it in there to totally fill the hole.
When cured, drill it as you would with any wood piece and drive in the
screw.  It will hold the screw.  If you no longer want that particular
hole, just sand it smooth.

This stuff is also great for replacing missing wood.  It sands and
shapes wonderfully and takes a stain.  I would suggest removing all
tracing of shellac, varnish, glue, etc. from the surrounding area and
screw hole before using.

A more traditional method would be to drill out the screw hole and fill
with a new piece of wood, making sure not to use end grain if you are
planning on putting a screw into it.  If you are just filling an
unwanted screw hole, drill it out and glue in a piece of dowel rod.

Jim Quashnock