There are many ways to sand paint off metal, but an orbital sander and a sanding block are the most common tools to use. Orbital sanders do most of the hard work for you and are more efficient than sanding blocks. If you don't have an orbital sander, you can buy one for about $60 or just use a sanding block. Sanding blocks aren't bad, but you need more time and elbow grease to use them.
Attach an 80-grit sanding disk to your sander and begin sanding the metal surface from which you need to remove paint. Because 80 grit is pretty coarse, stop using it when the paint is almost all the way off. This way you won't sand too much into the metal and weaken it.
Remove the 80-grit disk from your sander and replace it with a 200-grit disk. Finish sanding off the paint with the new disk. The 200 grit will give your metal a smoother finish than the 80 grit and won't dig into the metal as much.
Use pieces of loose sandpaper to reach any tight spaces where paint remains on the metal. Sand by hand with 80-grit paper, then 200.
Use steel wool to give the metal a smooth finish. Rub the steel wool in circles over the metal. If you're happy with how the metal appeared after you sanded it, skip this step.
Attach a piece of 80-grit sandpaper to your sanding block and start sanding the metal with a back-and-forth or circular motion. It doesn't matter which direction you sand unless you have a preference on how the sanding marks look.
Switch to 200-grit sandpaper when the paint is almost all sanded off, just as if you were using an orbital sander. Sand off the remaining paint.
Use pieces of 80- and 200-grit paper to sand off any paint the block could not reach. A sanding block is easier to maneuver into tight spots than an orbital sander, so this step may not be necessary.
Rub the steel wool on the metal in a circular motion to give it a smooth finish.