Most states do not require a sole proprietorship to register with the state business registrar to operate. All a business owner has to do is start running the business, as long as it is operated under the owner's name and not operating in a regulated industry. Writing a business plan for your sole proprietorship will help you keep a firm focus on goals through the startup period, and will help when you are seeking credit or financing for your business, but it is not a legal requirement. Maintaining separate ledgers that document your sole proprietorship business income and expenses will help significantly at tax time, but these are also not a legal requirement of forming a sole proprietorship.
If you want to operate your sole proprietorship under a name other than your own legal name, most states require that you first register the name as a DBA -- "doing business as" name -- with the appropriate state or local regulatory agency before opening for business. A fictitious name associated with the product or services you sell will help you brand and market your sole proprietorship, even if your personal name remains part of the DBA. For example, Mary Smith Custom Sewing better conveys the nature of your business than just using the name Mary Smith.
A sole proprietor operating a business in a regulated industry is typically required to obtain professional or occupational licenses from the state before opening for business. Professionals like lawyers and architects, as well as individuals working in regulated fields like cosmetology, tattoo artistry or mortuary services, need professional licenses from their relevant state agencies. Other types of businesses may require transportation or hazardous waste permits. Construction of a new store or office, or conversion of part of your home into a business, may require local zoning or building permits. These regulations may also put restrictions on parking, lighting and signs for your sole proprietorship.
If you are going to hire employees to work for your sole proprietorship, you will need to obtain an employer identification number from the Internal Revenue Service. You will also likely need to register with your state tax agency before hiring employees or selling products for which you must collect sales tax. You will need to pay self-employment taxes on any profit your sole proprietorship generates. To do so, report your income and expenses as a sole proprietor on Schedule C, Profit and Loss From Business, of your personal Form 1040 federal income tax return and its equivalent at the state level.