How do I prevent someone else from using a trademark similar to mine in the U.S.?

There are several ways to prevent third parties from using your trademark. Depending on the factual situation, the Trademark Office may or may not be the proper forum. You should consider contacting an attorney, preferably one specializing in trademark law.

The U.S. Patent and Trademark Office’s (USPTO) examining attorneys do not consider trademark use dates when examining applications; however, the USPTO's Trademark Trial and Appeal Board (TTAB) does consider who is entitled to registration depending on who has superior use in commerce dates. If your dates are prior to the other party’s and you can prove it to the TTAB, you have the opportunity to do so - through opposition proceedings as well as through a petition to cancel the mark once it has registered. You may also file a trademark infringement action against the other applicant to get an injunction against them to stop their use of the mark. You would have to prove that you had superior rights to theirs. Trademark rights, under U.S. law, accrue through use of the mark in commerce and not through registration. A USPTO registration is an evidentiary presumption that the registrant is the owner and has the right to use the mark. However, that presumption can be rebutted in court by one who has prior use of the mark in commerce.

Local bar associations and the yellow pages usually have attorney listings broken down by specialties. Time can be of the essence. Information about proceedings before the TTAB is available here.