Support - If somebody is willing to support you through any problems and/or nasty situations life throws at you, they are definitely what I would call a 'good friend'. We all need a shoulder to cry on, even if some of us won't admit it.
I'll Be There - A good friend will always be there for you when you need them. They may not be able to come over to your house and physically be there, but they will always be a phone call away.
Well, You Don't Have To If You Don't Want To - Another thing that a good supporting friend should do is never try and peer pressure you into doing something you don't want to do. They should support you in whatever decision you make, whether it be to do whatever you've been asked to or completely reject the offer. They should stand by you no matter what!