The very essence of a "good" friend gives the impression of "good" things taking place. And that wouldn't include things that are illegal or harmful. So what are the qualities of a "good" friend? We need to know this so that we can not only BE a good friend, but know what to look for when searching out good friends.
For example consider these questions: Would a Good Friend allow his buddy to drive drunk? Would a good friend drive drunk when his friend is in the car?
1) They influence you to DO and BE good.
2) They challenge you to DO and BE more.
3) They make you a BETTER person.
4) They PROTECT you from evil. (This would include all things illegal & harmful ... including people!)
5) They are HONEST.
6) They are TRUSTWORTHY.
7) They have your BEST INTEREST at heart.
8) They ENCOURAGE you to achieve great things.
I highly recommend you find people like this, and extend them the hand of friendship. As well you should be this kind of person to your friends.
Be a good friend, and find good friends!
Disclaimer: I realize you can not make people do anything! And as a friend sometimes we want good things for those around us, but in the end we are each accountable for the choices we make and what we do with what we have been given.
One day I believe we will all stand before a Holy Righteous God and give account for everything we've done that we shouldn't have done, everything we haven't done that we should have done, and every word we've ever spoken will be reviewed. If that scares you, good! It should, it scares the Hell out of me! But don't we want to be and do good because it's right? Not just because we will give an account to God some day, but because it is what is right. I do!