Not all states require a business license. The short version is to research local requirements.
That being said,

, check out your secretary of state's website and your city's website for business regulations. You may also wish to visit the Small Business Administration's website (
www.SBA.gov). You should also go to the IRS website (
www.irs.gov) and check out the small business section.
Another important issue is setting up/maintaining good accounting records, which can then be sent to your accountant at year-end to properly file your taxes.