If you're buying a used piano:

Don't leave home until you measure the front door. There are few things in life so frustrating as trying to fit a 37-inch deep piano into a 36-inch doorway.

Play every note on the keyboard. No one will listen to you play Beethoven's Minuet in G, if your G has jelly in it.

Find out whether the piano bench and delivery costs are included. Either of these essentials can significantly alter the cost.

Consider taking a pro with you. A piano technician will run you $50 to $100, but the advice may save you that much in the long run.

Be aware of size limitations. Time spent looking at grand pianos when you live in a loft is time wasted. Sizes: spinet, 36 to 38 inches high; console, 39 to 43; studio, 44 to 49; vertical grand, 50 to 62; grand, 5 to 7 feet long; concert grand, 7 to 9 feet.

According to Passion for the Piano by Judith Oringer (Tarcher, $8.95), these are some of the most reliable acoustic piano manufacturers: Aeolian, Baldwin, Everett, Kawai, Kimball, Sohmer, Steinway, Wurlitzer and Yamaha.

Other sources: The Piano Owner's Guide: How to Buy and Care for a Piano by Carl D. Schmeckel (Scribner's) and the free pamphlet, "The Consumer's Guide to Buying a Piano," published by the National Piano Manufacturers' Association, 15080 Beltwood Pkwy. East, Suite 108, Dallas, Tex. 75381. (214) 241-8957.

Other notes:

You're apt to get the best deal from a private party, especially if the seller has a 500-pound piano, is moving to Alaska and you're sitting in his living room waving cold, hard cash.

If you are a beginner, consider renting. Many rental programs allow you to put six months of rental fees toward the purchase price of a piano.

Piano practice rooms can be rented at the YWCA for $3 an hour. Call (202) 638-2100.