Witness a crime, or have information crucial to the successful prosecution of organized crime, drug trafficking or other felony. For the U.S. Department of Justice to accept you into the Witness Protection Program, you must be willing to follow through with testifying, and realize that once you change your identity, you won't be able to go back to the town where you used to live or contact any non-protected family members.
Know that once you are accepted into the program, you will receive 24- hour a day protection from U.S. Marshals until the trial is over. They will also assign you a new identity and relocate you to a new city.
Testify against the accused criminals. This is the most dangerous time for a person who'll be joining the program. U.S. Marshals go to great lengths to protect the witnesses, often sneaking them into court while providing a diversion elsewhere to throw off anyone who might be planning to cause the witness bodily harm.
Assume your new identity in a new city. While you will be given monetary assistance for a period of time, plan to find a job with the assistance of the government within a reasonable amount of time. Once you have assimilated into your new identity, plan to check in with the government once a year or if you move.