To develop the best credit score by using a credit card, you should use it at least once a month for something that you need to buy anyway (gas, food, etc.). Set that money aside immediately so that you have the full amount when the statement arrives.
Pay in full, but don't pay before the statement prints. If you mail in your payment or pay on line before the cycle closes (so that you have a zero balance when the statement prints), it will appear to the credit bureaus that you aren't using the card - which will not help your rating.
But, you should always pay in full once the statement prints, but before the due date. That way, you'll never pay interest.
Keep your utilization at, or below, 30% of your available credit to develop the best credit score. In other words, if you have a $1,000 limit on your card, you shouldn't have more than $300 showing when the cycle ends. If you're going to be over the 30%, then it would be good to pay it down before the cycle closes - just don't pay it off until you actually get a statement in the mail (or it shows online as having closed if you go paperless).