First, focus your usage on 1 (or max 2) credit card. You want to build a long term history with this credit card, and you want them to know your purchase habit. This way, they can do more preferential things for you, and they can protect you better.
Go to your credit card companies' website and setup whatever fault alert they offer. Also use paperless monthly statement, so nobody will steal your information from your mailbox (plus, it is environmentailly green).
Second, you want to keep a close track of all your credit card. Every 4 month when you do your credit report check (see Sec 5.4), you want to make sure that you recognize the historical usage and payment of all your credit cards.
And, most importantly, pay in full on time every month.
Do those simple things, and you will enjoy your credit card and a good credit score.
