Once you're content with your trademark search and you feel confident that you can use the trademark you want without infringing on anyone else's rights, the process gets easy. It's easy, but it costs money (there's no avoiding this), and the application won't be processed for a long time.
There are two types of application you can file (there's another one for non-U.S. applicants, and you can find out about more about that at the USPTO's website). The first is the "use" application, which is the one you complete if you have already begun using the trademark in commerce (see the next paragraph). The second is the "intent-to-use" application, which you complete if you have not yet used the trademark but you have a genuine intent to use it. If you're confident there won't be any problems with your application, go ahead and start using the trademark, then complete the "use" application. The USPTO won't register your trademark until you use it and submit an "allegation of use" to them, so if you complete the "intent-to-use" application, it means more paperwork for you later (you have to send them the allegation of use within 6 months, or up to three years if you apply for a series of extensions).
The use of a trademark "in commerce" refers to the Constitutional grant of authority to Congress to regulate "interstate commerce." We're not going to go into it, because most of this legal stuff is brain-dryingly boring, but Congress liked the idea of using this power really broadly, and it's not tough to fit under it. The USPTO defines "interstate commerce" in this way: "For goods, 'interstate commerce' involves sending the goods across state lines with the mark displayed on the goods or the packaging for the goods. With services, 'interstate commerce' involves offering a service to those in another state or rendering a service which affects interstate commerce (e.g. restaurants, gas stations, hotels, etc.)."
Whichever type of application you decide to complete, before you apply, try to determine ahead of time whether the application will be accepted. In addition to the requirement that nobody else be using the trademark you want to use (or something similar), your trademark must also be distinctive. That means it cannot be so generic that it just describes the product instead of the source of it. For example, if you sell timber, you cannot trademark the word "wood" or "timber," but you could trademark "wood-o-rama" or "timbermania." Furthermore, the USPTO will not register a trademark that contains:
* names of living persons who have not given their consent * the U.S. flag * other federal and local governmental insignias * the name or likeness of a deceased U.S. President without his widow's consent * words or symbols that disparage living or deceased persons, institutions, beliefs or national symbols, or marks that are judged to be immoral, deceptive or scandalous
Again, if in doubt, talk to a lawyer. We don't mean to harp on this, but seeing a lawyer doesn't necessarily mean you're going to break the bank. Let's say you're willing to do a lot of the legwork yourself, but you're not sure whether the somewhat similar trademark you found in your trademark search (see Step 2) is substantially similar, or whether "wood-o-rama" is immoral or scandalous. Take your specific questions to a trademark lawyer, and she will probably be able to answer them in relatively short order. You can find a trademark lawyer in the Yellow Pages or on the Martindale Lawyer Locator.
Once you've answered all of these questions to your satisfaction, there's nothing else holding you back. Go to the USPTO website and click on "Trademarks" in the left-hand column. There, you will find the application forms, plus instructions and much helpful information.
