In the US, having debt is seen as a good thing, as long as you stay current on payments. Not having debt gives you a lower credit score than having debt, which send kind of fucked up to me.
However, using more of your cards' limit (a high debt utilization ratio) actually reduces your score.
On-time payments are only one factor in your score. Depending on the model it may only account for 20-30% of the score. Using your cards a few times a year may satisfy the criteria. You don't have to take on any debt to have a high credit score.