One of the myriad items to consider when starting a new business is what to call your company, what logo to use, and how to prevent others from copying your ideas. Especially for tech startups reading this blog, I want to give a few quick thoughts on trademarks for you to consider as you begin building your brand.
A trademark identifies goods or services as your own; it lets consumers know the origin of a good or service is you--not some third party. In the U.S. you obtain basic rights in a trademark simply by using it. That said, there are distinct advantages to registering trademarks with the U.S. Patent and Trademark Office (see below). Trademarks are not the same as registered business names / assumed names, which are just the name under which you do business (as may be registered typically with the Secretary of State's office). Trademarks are not the same as web addresses (although a trademark incidentally--if you're lucky enough!--be a web address).
When selecting your mark, you ideally want something that is fairly unique, that is not similar to the mark of another party. Using a mark that is too similar to another's trademark poses a real risk of a trademark infringement suit (which may lead to you having to pay money damages). Don't be generic. Generally, I recommend against last names (since they may require secondary meaning to be of much value). I also strongly discourage descriptive marks (e.g. "the running store" or "the data vault") since they too can be a lot harder to protect. If you can, try having an arbitrary or truly unique (possibly nonsensical in ordinary English) mark, since they are the easiest to protect.
Before you use your mark, definitely perform a trademark search to make sure the mark isn't already used. Any competent trademark attorney can do this and issue a legal opinion on the risks of using the mark, whether the mark is even eligible for registration, what kind of costs you should expect to be involved, how to "police" third party uses of the mark, etc. Registration is really valuable: while you don't necessarily have to have your marks registered with the USPTO, registration greatly expands the geographic scope of the rights you obtain.
Talk with your attorney about when to apply for USPTO registration. Applications when a mark is in commerce may be slightly less expensive tan applications in advance of use in commerce. For cash-strapped startups, that might matter (especially if you foresee multiple applications / multiple marks). Also, at the end of the process, make sure you establish protocols for "policing" your mark (as mentioned above). Failure to make sure others do not wrongfully use your mark may jeopardize your legal rights to the mark.