Being a good listener is essential to be a good friend. if your friends feel as if you are not listening or have no interest in their lives they will not confide in you. Without the ability to listen your friendships will be superficial.
Being compassionate is important quality in a good friend. Being able to sympathize regardless of weather or not you agree or disagree makes you the go to person in a crisis.
Not enough can be said for loyalty in a friendship. A good friend should not steal your exes, talk behind your back or betray you in any way.
Trust is another quality that is important in friendship. You should be able to tell your friend all your secrets and know that they will go to their grave with them if requested.
Being supportive makes you a good friend as well. Knowing that you friend will stand behind you regardless of what you choose is important.
Honesty is absolutely essential to maintaining a friendship. If you can't trust your friends to tell you the truth, they shouldn't be your friends.
Being a comfort to your friends in their time of need is important as well. You friends need to know that you will give them a hug when needed or come over on a moments notice to eat ice cream.
Reliability is really important to being a good friend. If your friends can't trust you to show up for their important events, it can sometimes negate your other good qualities.
Being fun and share your friends interest. Having a good time with your friends over the years, creates the memories that last you a lifetime.
Love is another important aspect to longevity in friendship. After being friends with someone for years they should be like family to you.