Keep in touch: Don't let long silence and lack of contact ruin your friendship. Keep in regular contact, such as once a week or once a month, in order to understand each other's life and recent situation.
Share with each other: sharing each other's hobbies, plans and goals, as well as some interesting things in each other's lives, can enhance your understanding and affinity.
Make plans: If you want to keep in touch, you can make some plans, such as watching movies or reading books together, or making some common goals. This will help you keep in touch and enhance intimacy.
Use more video calls: You can get to know each other more intuitively through video calls, similar to the usual face-to-face chat. If time and place permit, you can try to communicate by video call, which can better maintain friendship.
Message reply: If you can't chat at the same time, you can try message reply communication. This way, even if you can't communicate online at the same time, you can reply to each other's information in time.
Most importantly, it takes time and effort to enhance friendship with friends, but as long as both of you are willing to maintain this friendship, your friendship will be stronger.