How to make a lot of friends?

every year i tend to only cling and hang on to one "best friend" it happens all the time and when they leave the picture they have so many friends to go to. and im left feeling like a loaner...how can i make a lot of friends each day like for my sophmore year? and how do i become more social and have more than only one friend to go to? like how to i make a bunch of friends and keep them ? i just want to be able to call up my friends during the summer and be able to hang out and right now i honeslty don't think there's anyone i CAN do that with except for my family, and thats still not fun. how do i become more social? thanks!