If you have a really small business -- with only one to three employees -- you do not have to worry about the vast majority of antidiscrimination laws. The major exception to this general rule is the federal Equal Pay Act, which applies to virtually all employers, regardless of size. For a description of the Equal Pay Act, see Nolo's article Federal Antidiscrimination Laws.
In addition, there might be a local ordinance or state law that does apply to you (although the majority of these laws applies only to employers with five or more employees). To find out what your state laws prohibit, contact your state fair employment practices agency or check out Nolo's state-by-state resources, Employment Discrimination in Your State; ask your local government for information on municipal or county ordinances.