Make an effort
Be there. If you want to keep friends you have to make an effort. It's give and take. Yes, you can connect with new technology like Facebook and twitter, but it's not the same as being there. Personal contact lets friends know you actually do care and you are prepared to spend time on them. Email is easy, but physical presence says more. And when you are with your friends, switch off the phone sometimes. Don't check Facebook or your email or be constantly texting. It lets them know that you are concentrating on them, not your other friends.
Be helpful. Friends don't normally want anything from you except your company. But helpfulness adds to friendship. A strong wish to help is very attractive to other people. This could be anything from helping paint your new house or giving advice on where to go in London. Help, offered without anyone having to ask for it is always appreciated and remembered. And give freely. Don't try to measure it. Take as much as you need, give as much as you can.
Three little words
Be honest. True friends are people who can point out what you are doing wrong. A friend can tell you things which would be unpalatable from a stranger. The actor Charlton Heston said the secret to a successful marriage was three little words: 'I was wrong'. It's the same for friendship. If you value a friend then they just might be the only one who is prepared to tell you the truth.
Be happy. Yes, there will be times when you are very down and your friend is a good shoulder to cry on. But don't abuse that. Miserable people spread their misery and it's very off-putting. Don't get in the habit of moaning. Everybody is having a struggle through life. Smile. It will make you more attractive and the person you smile at will, subconsciously anyway, think it's pleasant to be around you. And be nice too and say nice things about other people. It will make you more fun to be with.
Be supportive. Everybody is an individual. Don't assume that other people view the world in the same way you do. Don't impose your standards on your friends. They will make mistakes, just as you will. Try to work out what they are thinking, rather than try to argue them round to your point of view. And when they've done something you admire, always give praise. It will boost them and keep them closer. As the song says, you've got to have friends...