Remove any old carpet or other flooring that's on your staircase. If your staircase is covered with carpet that's secured by tacks, put on a pair of gloves and use pliers to pull the tacks out of the floor before pulling the carpet back. If your flooring is secured with adhesive, you may need to apply an adhesive removal agent before removing it from your stairs.
Inspect your staircase to make sure it's free of nails and tacks. Remove any tacks or nails with your pliers. If you can't pull any out, hammer them below the surface of your stairs. Any tacks or nails that are left protruding from your stairs will damage your sander.
Remove any paint, varnish or stain from your staircase with an orbital sander. You'll need medium-grade sandpaper to remove any finish from the angled sections of your stairs.
Purchase the appropriate paint or varnish your staircase. Either way, you'll need to buy a product that's been designed specially for floors. Standard paint or varnish will not be strong enough to withstand the footfall your stairs must endure. You'll also need a primer to apply to your staircase before adding your finish.
Protect the area around your staircase with masking tape and then apply a coat of primer. Once this has dried, apply a second coat.
Apply a first coat of varnish or paint, allow to dry, and then apply a second coat.
Sand down your staircase's balusters and newel posts with a medium-grade sandpaper. If your balusters and newel posts don't feature ornate detailing, you may be able to sand them using an orbital sander. Finish with fine-grade sandpaper.
Protect your staircase, and any wall area close to your balusters and newel posts with masking tape.
Apply a coat of primer to your balusters and newel posts as directed by the manufacturer of the treatment you're using. You can use a standard varnish, paint or stain, as your balusters and newel posts don't need to be as hard-wearing as your stairs.