Hardwood floors generally will be topped with a layer of hard gloss (varnish or shellac in the old days, polyurethane today) which protects the wood from moisture and damage. The gloss will wear and become dull over time. If the floor itself isn't worn or damaged, you can restore the shiny gloss finish without doing a full re-sanding down to the wood grain. Screening the floor, rather than fully sanding it, takes off just the gloss and just enough of it to apply new gloss layers.
Things You'll Need
Oscillating floor polisher
Sanding screens of various roughness (60-grit, 80-grit and 120-grit)
Floor-gloss applicator (looks like a push broom but is covered with cloth)
Load your floor polisher with a 60-grit sanding screen. Starting in one corner, screen the whole floor, running the polisher forward and back in the direction of the floorboards. Do the entire room.
Repeat the process with the two finer levels of sanding screen (80-grit and 120-grit), vacuuming between each screening. The floor should end up looking smooth and dull, with no shine.
Go over the entire floor with your tack cloths to pick up any remaining dust.
Pour down a line of polyurethane gloss near the corner furthest from the doorway, pouring it so it goes across the width of the floorboards. Make the line as long as your gloss applicator.
Set the applicator in the gloss and slowly pull it backward in the direction of the floorboards, spreading the gloss over them. Pour more gloss as needed and continue spreading it, working in rows. Do the entire floor. Let it dry overnight.
Buff the dry polyurethane by hand with 220-grit sandpaper, using quick, light strokes, just enough to remove the shine. Vacuum up the dust. Go over the floor with tack cloths.
Add another layer of polyurethane gloss using the same process as the first layer. Let it dry, buff it, clean up the dust and apply a third layer. Let the third layer dry at least two days before using the floor.
Wear a dust mask when screening the floor and ventilate the room when applying your polyurethane.