The first common mistake is not checking to see if they have legal permission to use the business name. A business owner needs to check if it is infringing rights on an existing business. They should check to see if it's available and this can easily be done through a free name search or through Corpnet.com.
The second common mistake is when the wrong business entity is chosen to incorporate, such as choosing an LLC instead of a C-Corp or vice versa.
A third mistake is incorporating in a state other than where they are conducting business. Many people associate the concept of forming an LLC with states like Nevada, Wyoming or Delaware. As a general rule of thumb, small business owners with less than 10 employees should incorporate in the state that the business is physically in, otherwise, they will end up with two state filing requirements.
Once an LLC or C-corp is formed, the business owner's job is not done and not keeping a corporation compliant is the fourth common mistake business owners make. This can have severe tax implications and put the LLC in bad standing and risk being administratively dissolved by the state. Annual filings must be done and can easily be done through a website like Corpnet.com.
Lastly, it is important to register the business DBA through the state or county of business.