Here's what the USPTO says:
"Trademark applicants and registrants should monitor the status of their applications or registrations in cases where a notice or action from the USPTO is expected. Inquiries regarding the status of pending matters should be made during the following time periods:
(1) During the pendency of an application, an applicant should check the status of the application every six months between the filing date of the application and issuance of a registration; and
(2) After filing an affidavit of use or excusable nonuse under §8 or §71 of the Trademark Act, or a renewal application under §9 of the Act, a registrant should check the status of the registration every six months until the registrant receives notice that the affidavit or renewal application has been accepted."
I respectfully disagree with the USPTO's assertion to check your status every 6 months. While the entire registration process can be poky, it's better to stay more on top of your filing. At TradeMark Express we recommend to our clients that they check their status every two weeks to one month. This way if the USPTO had, for instance, sent you an Office Action that needed a response, you'll have plenty of time to deal with it.
To check your status, go here and enter your Serial Number. I'll devote tomorrow's post to defining common status descriptions.