Decide on the look you want first, so you can determine whether to sand and stain the door like we did, or whether you want to leave it as is.
Start by removing any old hardware, such as hinges, knobs, and plates.
If you plan to paint the door, simply scrape away any loose paint or finish, and then re-coat the wood.
If you plan to stain, use stripper if necessary to remove old paint or finish, and then sand the wood. Start with 100- or 120-grit sandpaper, and then go to 150-grit, and finally 180-grit.
Then clean up the glass using a razor blade and glass cleaner.