Removing Set-in Grease Stains?
Spray wd-40 on the stain, let it sit for 10 min, then rinse it out with water. Follow with a laundry pre-treat stain remover (Spray n Wash, etc), then launder.
Staining Wood Furniture?
If youre only stripping off the varnish, make sure you get it all! Otherwise the stain wont soak into the wood as well. I have always gotten the best results when stripping everything off, even though it takes more work.
Cleaning Old Bathroom Cabinets?
Try Restor-A-Finish. You can buy it for about $7 at Home Depot. When you rub it on it takes water marks and scratches right out. I used it on my kitchen cabinets and a coffee table I bought on Craigslist, which looks brand new now.