TIP 1
Though it would be hard to find anyone willing to hand scrape a floor in our time, the principles behind scraping and filling still apply to many old-house floors: For old or new work, sand down to the finest grit practical in stages to remove mill marks, moving from, say, 80 grit to 220 grit. Vacuum meticulously between sandings, and don't make wide leaps between grits. Traditional wood fillers are still available for fine woodworking (albeit increasingly in altered, clean-air formulation) and can be an option for new open-grain wood floor installations. Test first to judge results.