I decided a few years ago that I was going to check my credit report regularly. Each person is allowed to check once per year with each of the three agencies, and rather than pull them all at once, I like to spread them out. Combined with my wife, we can pull a credit report every other month. So, if you pull reports in odd months (January, March, May, etc), you'll be following my plan.
While there is a commercial with a catchy tune and funny costumes, regardless what they say their credit report isn't free. You end up signing up for a service. Instead what you want to do is go to www.annualcreditreport.com. Once there, you'll fill in your state, then some basic information. One option I highly recommend specifies that on printed reports, only the last 4 digits of your social security number are printed. You may not print your reports (I do), but there's no sense printing on paper, on disk or even on the screen your full social any more than required.
Next you'll select one of the three agencies. This could cause some people some grief. "Which one do I pull first?" you might be saying. The answer is simple - any one you want. If you haven't pulled a report in the last year, my suggestion is to take the one at the top. If you've pulled that report, take the second on the list. The order may change, so don't count on it being the same next time, write down which report you pulled.
Once you've selected an agency, you'll be taken directly to that agency. Here you'll be asked some questions to verify that you really are you. You may be asked about old addresses, old accounts, details on your mortgage or recent credit changes. It might be best to have access to your records at this point, to know what your mortgage payment is, who your banker is and where you have accounts.
Once you get your credit report, you should review it carefully, If you find mistakes, you should call to find out details on the mistake. If you want the information corrected, don't settle for a call, write the owners of the account. My approach is to write to the owners first, then write to the credit agency if I don't get resolution. You could write to both at the same time.
I keep a copy of the credit report, at least until I pull another one from the same agency (a year later). You may decide not to keep a copy on paper, but I'd recommend keeping a copy on disk in that case.