get something that has no annual fee, for starters. nerdwallet has (or at least used to) have a good tool for looking at offers based on credit score, including options for people that have no credit history.

anyway, the main thing is to get something that is taken everywhere (not amex, not discover), gives you some kind of benefit (1% cash back?), and then use it for all of your purchases, and then pay it off completely each month. pay off the full balance, not just the statement balance. i have been using Mint to track my accounts, but that is going away and i haven't figured out an alternative that meets my needs yet. it is very convenient and helpful to have an app on your phone that lets you look at your statement balance in real time and look at transactions. you can usually have it generate reports to see where your money is going. more importantly, it gives you peace of mind to know that if a fraudulent charge shows up, you can immediately call and have it flagged. though that's rare. sometimes an app is offered by the credit card bank, but there are free alternatives.

anyway, open an account, stop carrying cash, and keep that account at $0. or, you can literally just activate the card and keep it in your sock drawer.