You have to be truthful and trustworthy. You have to be there for your friends and always have their back in tough times. You have to be willing to be able to stop them and get them to see if they are doing something bad. You have to be nice to your friend too. It takes a lot to be a GOOD friend.
Be honest, trustworthy, nice, nonjudgmental, a good listener, and always there for them. A good friend is able to loo past people's lil quirks and flaws and still love them more than anything and always be there for them. :) hope this helps!