Wrap a measuring tape around the stair spindle at its narrowest and widest diameter. Write down the two different measurements.
Cut a strip of 80-grit sandpaper. Make it 2 inches longer than each width you wrote down in Step 1 by 1 inch wide with a pair of shears. Cut another strip of sandpaper the same length and 2 inches wide. Cut another piece of sandpaper of the same length and 4 inches wide. Repeat with 200-grit and 300-grit sandpaper, respectively. This gives you a large palette of sizes to choose from when you're sanding, which is ideal for intricately carved stair spindles.
Wrap a piece of 80-grit sandpaper with a 1- or 2-inch width around the narrower or more carved parts of the stair spindle. Rub sandpaper back and forth, removing all the old finish. Wrap a 4-inch wide piece around the smoother and less detailed parts of the spindle. Rub it back and forth, removing the old finish. Repeat with your 200-grit and 300-grit sandpaper.
Wipe down each stair spindle with a tack cloth to eliminate the dust from sanding.