Summarize this article in one sentence.
Talking is the best way to keep a friendship alive and stay in someone's mind. Make time in your day to catch up with old friends so that you have things to talk about when you meet up again. Don't feel like you need to share everything or talk once a week. Simply taking an hour every now and then to chat is often all you need to do to keep a friendship alive. Sending a card or message to someone on their birthday shows them that you still value their friendship. Even a quick note to celebrate an old anniversary, like the day you graduated together or started your first road-trip, can bring up shared memories that keep your friendship alive. Best friends remain friends because they have a bond of trust that can sustain time and distance. This means sharing secrets, fears, and worries, and knowing that you will get good, honest advice in return. It also means keeping the secrets and stories of your friend to yourself. No matter how far away you are, you should feel like your friend has your back, and you should have theirs. Even a kind, considerate note can be enough to help someone in a tough spot. Good friends are there when the going gets tough, even if they haven't talked in several months. Offer to help with problems, support them in hard times, and show that you are a friend in the bad times as well as the good.

Summary:
Talk to each other once or twice a month. Remember big occasions, like birthdays or anniversaries. Build trust with each other. Help your friend out when they are in need.