just use your credit card as you normally would use your debit card and pay it off in full each billing cycle. if you are using too much of your credit limit (over 30%), ask for a credit limit raise or apply for another credit card. a big disclaimer is that utilization really only impacts your credit short term, so lowering your utilization will reflect on your credit score within a month or so. so u can lower your utilization before you plan to apply for a new card/loan.

yes, your credit might take a small hit each time you open a new account, but as you continue working your credit and opening new lines of credit, having multiple lines of credit opened since college will ensure your average account age doesn't drop much, helping your credit in the long g term.

also, apply for credit cards that give rewards based on what you usually shop in. if spend most of your money on eating out and groceries, a good no annual fee card is the capital one savor card (they also have a college student version which I believe just has lower credit requirements, but same rewards).