Your business name is your identity or brand. The name you choose is as important as the business you serve. If your brand is not your personal name, like Donald Trump, then you will have to do DBA (Doing Business As).
Research the name you want to do business as. If the name is so similar to an existing name that customers would get confused, you cannot register it. Check phone books, official records and, most importantly, the secretary of state website for the state you want to DBA in. It will not register your name if it is the same as another on file.
Get the required form from your county office
Fill out the Form Completely. If you change your mind about the business name, you do have to fill out another form.
Pay Fee (if applicable). This is usually just a small fee if you don't have the form.
Run the required notice in newspaper if required. In CA, if has to be run for within 40 days of filing. It is valid for 5 years. It has to be published 4 consecutive weeks with at least 5 days between notices, not counting the day of pulication.
If your name is unique, Trademark it: If the company will be local, you would just file with the Sec of State for a small fee. Getting a national trademark will cost at minumum $248.