I leave masking tape on the limbs as long as possible to prevent dings and scratches during shaping of the bow. This also keeps the centerline I've drawn on the tape visible throughout the shaping and tillering process.
So, when I go to apply the overlays, I peel off the masking tape only as far as I need to, to expose the gluing surface, then sand/scratch the surface with coarse sandpaper. I use 60 grit and go diagonal one way, then the opposite way. I then wipe with acetone or alcohol to remove any dust or residue immediately prior to glue up.
Once the entire bow is shaped, tillered, and ready for sanding with 240 grit paper, I remove the remaining masking tape and sand the shine off all of the glass with 240 grit, then apply the finish.