Most businesses have at least one trademark, typically a name that identifies the business in the marketplace. Selecting the right trademark, however, takes some thought.
It's generally not a good idea to select a trademark that simply describes the service a business is offering. For example, the trademark “Residential Plumbing Service” is a poor choice unless the business already has a large and well-established customer list.
Such trademark just doesn't uniquely identify the business to prospective customers. Furthermore, such trademark is completely impossible to protect from a legal standpoint. The trademark can't be registered, and no court will block other businesses from using the same trademark, particularly since any residential plumbing service will need to use those words to describe their business.
Some business owners choose to use their last name, or their full name, to identify their business. This is better than using a generic phrase to identify the business, although it may take some time before such a trademark can be legally protected. Such trademarks must, in legal parlance, acquire secondary meaning before they can be registered or enforced in court. Commonly, this takes five years or longer.
The best trademarks are trademarks that only suggest the nature of the business, or better yet, are a fanciful word or phrase. To continue the plumbing example, a suggestive trademark could be “Pipes and Such”, and a fanciful word could be “Plumbanator.”
Once you select the trademark, then you should check to make sure no one else is using it. A quick search on Google and Bing is a good starting point. After that, search federal trademark registrations on the USPTO website using the TESS query facility using the “New User” query. Also search trademark registrations for your state on the state's applicable website.
If no registrations turn up that are similar or identical to your trademark, then you should be good to go.
If you want to be extra cautious, you could then order a professional trademark search from a search service, which can in some cases turn up uses of your trademark that might not be easily found using the techniques I described above, such as, for example, local directories, or business name registrations for inactive businesses.
When you're sure you're ready to use a trademark, then it's a good idea to file a trademark registration application, with the USPTO if you're doing businesses across state lines, and with your state, particularly if you're only doing business in your state.