I have probably made around 15-20 sets of pistol grips.
1. Thickness the new grip blank.
2. Trace old grip onto the new grip. (It is best to secure the old grip with some electrical tape, and drill the mounting hole with a drill press)
3. Cut/sand to the line.
4. Shape the grip. If you have a big belt or disc sander. Use some double sided duct tape, and stick it to a larger piece of wood to use as a handle. Then contour of the sander. If not, you can just use files and sandpaper
5. Counter sink the screw holes.
6. Finish sand and polish - if wood, add finish.