Focus on what you can give to a friend, not what you can get out of a friendship.
If being happy is your only motive for wanting someone to be your friend, then you are not being a real friend. Don't get caught up in keeping tabs on who has given most to the friendship. Give to your friends regardless of how much they give to you. You can make your friendship strong by giving gifts to your friends. It is not necessary that you only give them costly gifts. For a real and true friend, even a card can be more precious than the costliest gifts.
Encourage your friends
Real friends inspire and push each other to be the best at what they can be, rather than drag each other down.
They are happy when their friends help them in their goals. You, too, should encourage your friend by bucking him up and by making him realize that yes, he can do it, and by giving him a strong supportive hand.
Be willing to forgive
Mostly friendships get feeble when there is no one willing to forgive. Due to this, the friendship crumbles and individual wounds turn to grudges. So forgive your friend and move on.
Tactfully point out their mistakes
Pointing out a friend's mistakes can also make him angry, but this is one way of showing concern for him. If you really care, tactfully point out his mistake for his own good. But once you've brought the problem to your friend's attention, don't harp on about it all the time.
Don't walk away
When you see some of your friend's faults be patient. Be patient as your friend tries to change. Realize that nobody is perfect.
First thing in a true friendship is to be honest and reliable. You must assure your friend that you will always be there for him/her. Likewise, you must not mistrust your friend because friendship is very vulnerable to distrust.
Don't try to control your friends
Real friendship does not mean you always have to be together. It may be tempting to have a fun person all to yourself, and you might feel threatened when your friend spends time with others. If you are afraid to let your friends out of your sight, you are probably afraid of losing them. Good friendship will endure time spent apart: you and your friends may learn to appreciate each other even more. So don't push your friend to spend all his time only with you. No one likes to be bossed around.
Be there for the good and the bad times
Friends are to share feelings with ... to share things which one cannot share with others, to celebrate with when you are excited - and also to share the downs of life with. Don't think that you are a friend only for the good times. When your friend is upset about something, you must give him your full attention. Lend your friend a sympathetic ear and understand his feelings; celebrate his happiness but also be a part of his sorrows.
Learn to accept personality differences
It is not necessary that your friend has to be exactly like you in personality, attitude and beliefs. Your friend can very well possess a different personality from you. So be careful not to expect your friend to be exactly like you. Accept and appreciate him for what he is - a unique individual, just like you are.
Don’t be blabbermouths
Sometimes, while talking to others, we get so excited that we spill our friend's secrets in front of others. This breaks your friend's trust (and rightly so too), and deteriorates your friendship. So learn to keep each other's secrets.
Don't let arguments destroy your friendship
Suppose you are having a discussion with a friend, and he disagrees with what you think is true. Don't keep arguing until you get mad at each other. Just drop the subject of conflict. Your desire to win the argument may ruin your friendship, so the easiest way of closing a controversial topic is to say, "Maybe you are right". Pointless discussions achieve nothing.