I don't check my credit report for wrong-doing or to find out my credit-worthiness, necessarily. I'm looking for good old-fashioned human error - something that was reported erroneously or incorrectly, such as a late payment or an account that shows open, even though I have requested that it be closed.
As far as my credit-worthiness is concerned, I guess, based on what I was told it was when I last took out a loan. If it was excellent then and I have no negative ticks and a reasonable amount of debt now, then I'll assume it has either stayed the same or increased.
If your credit is not excellent, then I'd at least try to get in touch with whomever reported negatively and fix any issues, if possible. With that said, I've never personally had to go through fixing a mistake or minimize the impact of a very negative report; however, I am close to some one who has. It took over a year and persistence to get it fixed, but that person's credit has improved drastically since, allowing for establishing "real" revolving credit (credit cards) instead of "starter" accounts with very a very limited line of credit and no real benefits.
So, I highly recommend every one check their report or issues. I found a "late" payment once, but hadn't checked my report in so long that it wasn't worth it to try and fix it. Had I been trying to obtain a mortgage or any other expensive loan at that time, who knows, it may have negatively effected me to the point where I'd have to consider pushing off taking out the loan until the issue was corrected.