1) Don't buy anything with the credit card that you wouldn't buy otherwise. The credit card is not to help you buy more stuff. It is to help you build credit, get rewards, have the safest possible transaction, smooth transactions that are otherwise a hassle, etc.
For example, I had a friend in high school who finally got his credit limit above $1000 and instantly bought an engagement ring (he was 18 years old). I asked him why so soon. His answer was since he had the credit limit. That is possibly the very worst reason to propose marriage that anyone has ever had. (The marriage failed within months).
2) Forget about rewards. I'm not saying get a credit card with no rewards. But once you get that card forget about them. Studies show people spend far, far more if they think about credit card rewards. They think "oh, I'll get a whopping 1% back, so I can afford this!" or "I can splurge on this since I'll get 50 airline miles!". Don't fall down that trap (see #1).
3) Pay the credit card in full. Don't pay the minimum. Don't pay between the minimum and the maximum. Pay the maximum. Every month. There is no better way to build credit. There is no other way to avoid interest or other costly expenses.
4) Pay the bill the day you get the bill. There is no "forgetting" that way. There are no fees for late payment that way. There is no interest to pay that way. If you don't have time to pay bills that day, don't get the mail.
5) Set up your credit card to have the minimum amount paid automatically every month (or set your bank to pay the credit card the minimum amount each month whichever you prefer). This guarantees that you have no late fees and guarantees that your credit score only goes up. But still see #3, and pay the full amount yourself each month.