Here are a few tips for refinishing a hardwood floor: 

Remove furniture, rugs & curtains from the area to be sanded.
Remove base molding & tack strip and sweep the floor.
Be sure all protruding nail heads are counter sunk before starting.
    Equipment needed:

• Floor Sander
• Edger Sander
• Sandpaper (Coarse, Medium & Fine)

Place the sander in position so that the first pass is made diagonally across the floor surface. Start with coarse sandpaper if the floor has a lot of old finish remaining on it. Use medium sandpaper if there is not a lot of finish left.  Sand the entire floor at the same angle and then repeat in the opposite direction. Never stop the sander with the drum in contact with the floor.  Use the edger sander to complete the areas the drum sander won't reach. 

Do not attempt to remove 100% of the old finish or imperfections with the first pass. The rest will be removed in the second sanding.

Repeat as necessary. 

Sweep or vacuum the floor. Remove any dust with a painter's tack rag. Check the floor for any leftover imperfections and lightly hand sand. 

Follow the manufacturer's recommended application directions when applying finishes.

GOOD LUCK !