Dude it's easy. Well it's even easier if you have lots of friends.
Like going with some pals and sarging is cool, but I usually just go it alone.
I assume you are in HS. Well go up to a table of people, and say something like, "Can I eat lunch with you all?"
No crap like, "It's your lucky day, I am going to sit with you."
Because you aren't a pretentious prick.
I am talking about sitting at a table with a few guys, and a few girls.
As you meet more guys, you will meet the girls that they hang out with.
It is easy as pie. If you already have guy friends, then girlfriends will be easy.
Yeah just make an effort to met more girls, and the guys they hang with.
Girls like variety, and you should bring variety to the group.