True friendship isn't dependent on your saying "yes" all the time and overlooking your friend's faults. Of course, while you're tolerant of their idiosyncrasies, you'll also want to support your friends in their personal development.
For instance, if you feel a friend drinks or smokes too much, you can tell him so. Offer some words of wisdom. Most of all set a good example.
Love can be both tough and gentle in its attempt to further the welfare of a friend. If your motives are pure, your friends will always be grateful, even if they initially seem to resist your efforts.
Be polite to your friends. Thank them for their company and their help. Don't be afraid to say "sorry," or "please," when required. These three magic words can really help create harmony. They also show that you don't take your friends for granted.
Loyalty is one of the hallmarks of great friendships. Avoid gossiping about your friends and keep the secrets safe that were given to you in love and confidence. Trust is the basis of true friendships. Treat your friends like you'd want to be treated.
Trying to prove that we are right is the root of much of the disharmony we see around us. Arguments can make us feel angry and resentful. Instead, just say what you have to say calmly and let it go. Letting go isn't the mark of weakness. It's a sign of greatness and humility.
Agree to disagree. If you must argue, ensure the issue is important and your motives are correct. You're not out to prove you're right. You just want to discover the other person's point of view and share your own. Most of all, you want your relationship to be better off for having had the conversation, just like they do.