I could explain in great detail the why and wherefore, but to make it simple for you:

Use the card for everything you can. Pay it off in full before the due date. If you're close to maxing out the credit limit before it's time to make a payment, pay it down early. During this time, your credit score will fluctuate dramatically. IGNORE IT.

In time, the credit limit on the card will increase as you prove to the bank that you can handle the credit responsibly. It will eventually reach a point where your monthly purchases reach about 20% of your credit line, which happens to be the upper bound of where the utilization factor of your score is. Example: If you always spend $1000 a month on the card, eventually (within a year or two) the credit limit on that card will probably increase to 5000. You might have to request the increase, or it might happen automatically. At this point, your credit score will stop jumping all over the place.

As long as the card has no annual fee, plan to keep it forever. You might at some point quit using it because there are better cards out there with more lucrative perks, but you want to use it to make a token purchase at least once per year to keep the account alive, because the average age of accounts is a moderate factor in your credit score and the the older the average gets, the better your score gets.

Seriously though, the only rules you need to follow: Never spend money on a card that you don't already have as cash in the bank, pay all bills in full and on time, and never close an account that has no annual fee. Do this and your score will take care of itself.