Here is a step-by-step guide on how to sand wood floors:

1. Consider the chance of lead. Many older homes contain lead in the floor finishes. If you are unsure whether your floor contains lead, you can purchase a lead test kit from a home improvement store.

2. Check for nails and staples. Before you begin sanding, check the floor for any nails or staples that may be sticking up. These can damage your sandpaper or even cause injury.

3. Rent a drum sander. You can rent a drum sander from a home improvement store. This is the best type of sander to use for sanding wood floors.

4. Install coarse grit sandpaper onto the sander. Start with 36-grit sandpaper and work your way up to 100-grit sandpaper.

5. Practice on a hidden area. Before you start sanding the entire floor, practice on a small hidden area to get a feel for how the sander works.

6. Decide where to start. Start in one corner of the room and work your way across the room in strips.

7. Sand at a slight angle to the grain. For the first stage of sanding, you can move at a 7 to 15 degree angle to the direction of the boards.

8. Move constantly as you sand. Keep the sander moving at all times as you work your way across the room.

9. Switch to medium grit sandpaper. By now your floor will be free of the old finish, but many scratches may still be visible.

10. Sketch pencil marks on the floor (optional). At this stage it can be difficult to see how effective the sanding is.

11. Start on the opposite side of the room and work your way back across in strips.

12. Sand at a slight angle again for this stage of sanding.

13. Switch to fine grit sandpaper (100-grit).

14. Sand again at a slight angle.

15. Vacuum up all dust and debris from the floor.

16. Apply stain (optional).

17. Apply polyurethane finish.