If you want to apply for a patent, the U. S. Patent and Trademark Office offers this advice:

Make sure your invention is practical before you spend a lot of money on patenting and trying to sell it.

Get a witness who can verify when you came up with your idea. If someone has the same idea, you want to prove you had it first. Under the patent office's Disclosure Document Program, you can send them a signed description of your invention and it will be filed for two years for $10 fee. Keep good records.

Have a preliminary search made in the patent office's search room to see if your invention already is patented. You can do it yourself, but because it requires skill and experience, most inventors hire practitioners, the patent office says.

Hire a registered attorney or agent. He or she can help you write the application as broadly as possible for your protection. $ patent attorneys and inventors offer these additional tips:

Use caution when dealing with promoters who offer to help you sell your invention for a price. Ask for references. Check the Better Business Bureau.

Stick to one field. "It's a lot easier to invent when you work in a field you known thoroughly," says inventor Jacob Rabinow.

Be prepared to lose money, so don't gamble your mortgage or your children's education on striking it rich.

Be patient, have confidence in your ability and fight it through if you think you've got a winner.