Find out whether you need a license. Apply for and buy a license, if you are in a state that requires it such as California and Massachusetts.
Get a storefront to see clients in, or erect a booth in someone else's storefront for a split of the fees you receive. Set up a table on the sidewalk, if you can't get a storefront and there is a lot of foot traffic in the area.
Look the part. Dress the way clients expect a fortune teller to dress, specifically with traditionally Eastern European clothing. Wear a head wrap, and keep your clothing colorful.
Decide how to arrive at the fortunes. Use a set of tarot cards, a crystal ball, raw crystals, palmistry or some other method. Make an eye-catching display for the method you choose.
Build good word of mouth. Retain your clients, and you can have a steady business.