Hobbies

Hey there.
There are probably a billion hobbies out there that will get you into social situations. From the sound of it you're either in high school or college, so you're pretty much in the prime of your life.

If you want friends quickly: Join clubs that have activities that interest you (wrestling, chess, skiing, band, drama, etc). Also, just be generally nice to people, and try to remember everyone's birthdays and first names when you get to know them

If you want to get laid: Learn to play the guitar, or the drums (or make a rock band)

If you want something to do that will pay off long term:

Practice your writing skills, practice your drawing and art skills, and most importantly, learn to play an instrument. Knowing how to play an instrument will come in handy in the future, especially at parties and social gatherings. Guitar and piano are pretty popular, but if you're willing to make a very long term investment I'd suggest the violin or the saxophone (tenor or alto, depending on your preference)