Actually, your credit rating can go down if you have no debt. The way to make it go up is having debt and paying it on time. A good credit rating means "you pay your debts", where as no credit rating means, "we dont know". That's why alot of people say college students should get a credit card and use it for things like gas and groceries, or get a loan for a car at some point. Those things are generally easier to get (credit cards are a joke to get these days, and cars can be repossessed, so theres less of an issue for people with no credit history). If you read through the EPSQ, they ask you about debts that are delinquent by a certain amount of time (I forget if its around 60 or 90 days). These things show up on your credit report in big bold print.
It's probably not a bad idea to order a copy of your credit report anyway. It's a good way to understand exactly what other people are looking at, as well as keep track of your assets. I know the first time I got mine, I noticed an account listed that I had forgotten I even had.