if you're in the right states go to freecreditreport.com. you get it once a year - it doesn't show scores but it shows history and everything each agency has on you.
checking your own score does not hurt your score.
One of the ratios they look at is available revolving credit to credit used, i.e. I have $15,000 available on my cards (total) and I'm revolving $10k is not good, however I have $150,000 available and I'm revolving $10k, better, I have no revolving credit but a lot available to me is the best. That's just one ratio, however. Others include monthly payments v. gross income (stay well under 30%), other assets, how many of those damn department store cards (bad), if you've been applying for credit, etc.
While cancelling credit cards does hurt your ratio of used to available, at a certain point you should get rid of cards if they aren't being used so you can manage it better and minimize risk. I have over $150k in available credit cards, and I don't use much, so if I get a new one I cancel one I won't use again. If I don't use one, I don't keep it open. Don't just cut the card, call the credit card company and request to cancel the account. It shows up on your credit report as voluntarily closed by the user, and it doesn't hurt your score (other than that used/available ratio).
Beware - the scores you 'buy' from them aren't necessarily the scores they give to the bank. The only one that you can trust are your scores when applying for a mortgage - the bank is required to allow you to see that. You can't get the score they give to the bank yourself. I have no idea why. Also, the scores from the 3 credit bureaus are not on the same scale, so a 650 from experian isn't the same as a 650 from trans-union. You don't have a credit score, you have 3 or more of them depending on the who is ordering it and what you're ordering it for. it's very confusing. The only way to know for sure is to apply, which if done too much for different things is not good.
More research - a good reference is Michelle Singletary on washingtonpost.com - she's got a lot of good info.