Hi Chris When I redid all of my double-hung wood windows, once stripped to bare wood, I carefully sanded all wood, trying my best to bring back the sharp lines of the sash and muntin edges.
IMO, one of the common mistakes when repainting wood windows is to paint the sliding surfaces. Doing this will simply rub the surface paint off over time. What I do is use a penetrating oil to seal the wood.....tung oil seems to work well....but don't build up coats...just apply two, sanding between each. Then apply a small (single light swipe) of parafin wax to the sliding surfaces. Because wax attracts dirt, you should scrub the sliding surfaces every year with a strong cleanser, rub down with 4-0 steel wool and reapply a coat of oil...then when thoroughly dry, rewax. If you do this, your windows will always slide like they are brand new.
Just my approach...and I'm sure there are many others...(smile)