Right... I may be of some help.
My freshman year of high school I was friends with absolutely NO ONE at the time because Jr. High was a sad, disappointing 4 years of my life and my only friend had moved away.
During lunch one day I heard this upperclassman at the table behind me talking about something I shared an interest in, in this case it was Magic the Gathering. I approached him in a cool, calm way. Not, "ZOMG YOU PLAY MAGIC TOO!!1!11! WE SHOULD BE FRIENDSIES FOREVER!" just like, "Hey, I heard you talking about playing Magic, what kind of deck do you play?" and from then on I sat at the table and he's one of my best friends to this day.
So I have a list of advice:
-Pay attention to conversations around you and if you hear someone talking about something you're interested in and use it to talk to them in a non-absurdly, annoying way
-Be yourself, don't try acting "cool" to fit in with the "cool" crowd. Most of the time the "cool" kids will see through the ploy and the non-"cool" kids will think you're just a poser. (You're friends shouldn't be chose just to make yourself popular, so be with the "losers" group if you like those guys and don't care about what others think)
-Be nice to people. If someone is into something you're not then deal with it and don't be a dick about it; its their opinion, not yours (one of my friends really dislikes anime and a lot of my favorite bands, but he's a good guy and fun to hang out with)
-Finally, like many others have said, just talk to people like a normal person. I know its hard, I really do but getting past your timidness gives a great feeling. My life motto is "Its better to regret something you did rather than something you didn't do"
I wish you luck, one shy high schooler to another
EDIT: I'd like to add: Don't try showing off to people when you really don't know what you're talking about. Theres a freshman I tried being friends with but he just annoyed me beyond belief because he thought he knew EVERYTHING about rock/metal music yet he confused Five Finger Death Punch with Iron Maiden (and many other things, that's just the one argument I remember)