Don't disappear after meeting someone, instead start showing up frequently.
Participate in groups with people of common interests. It is the easiest way to make friends:
If facing difficulties in finding an existing group, just start a group by yourself based on something that interests you.
According to studies, the length of time you smile during a conversation directly affects your perceived friendliness.
Many studies show that most people want to be friends with kind people. So, always talp pleasantly and kindly to everyone.
This strategy sounds very calculating, but it is working like a charm. When you meet a new set of people, just set a goal of making three new friends.