Conduct a trademark search using the USPTO's Trademark Electronic Search System. If someone else has already registered your trademark, you may not register it. If a registered trademark is very similar to the one you want to register, you may want to alter your trademark. If, however, you have been using your trademark in commerce for many years, you may be able to assert ownership by right of first use. This may require the assistance of a trademark attorney.
Use your trademark frequently in commerce on the items that you plan to use the trademark on after registration. For example, if you are registering a trademark to use the mark on clothing, you should use it frequently on clothing. Use the "TM" symbol next to your item; this symbol denotes an unregistered trademark. You should also use this symbol after you file your trademark application until your trademark is accepted. Early and frequent use affords your trademark more protection, particularly if someone else has already registered a similar trademark or attempts to do so after you register your trademark.
Notify anyone who steals your trademark that the mark is trademarked. Send a "cease and desist" letter itemizing how long the trademark has been used in commerce and enclosing a picture of your trademark in commerce as well as the other person's use of your trademark. If you have not completed a trademark application, you may need a trademark attorney to help you assert your rights. If, however, you have completed an application and are merely awaiting trademark approval, you will have more protection.