Here's how I would start a respectable business in the United States:
Choose a business structure, such as a corporation, an LLC, or a sole proprietorship.
Choose a name for your firm and check with your state to see whether it is available.
Register with the state, typically through the Secretary of State's website.
Obtain an EIN from the IRS; it is required for employment or tax purposes and is free.
Depending on your area and industry, apply for licenses or permissions.
To keep money separate, open a company bank account.
Begin keeping tax and accounting records immediately.
Obtaining business insurance and a municipal or federal trademark is optional, but recommended if you plan to expand.