Don't put too much of an emphasis on trying to hook up. You'll look desperate and stalker creepy. Be about having fun, safe and sane fun that won't put you in jail.
Be yourself and hopfully you have a good upbringing. Of course if you really are a jerk, you'll make a change to who you are. There are certain qualities that people like. Honesty, transparancy are big ones. Also the ability to listen and promote conversation is much great then the ability to blabber.
The goal is to be someone who others want to be around. That's a good start.
Then you need to work on your interpersonal communcation skills and overcome your fear of rejection.
I suggest reading How to Win Friends and Influence People. It's changed many people's perspectives including my own.
However at your age hormones and often the cruelty of others will make this difficult. If hormones is a problem, vigorous excercise is one thing that helps keep your thoughts leveled.
Also the part about friends. That's a line that you will hear forever and a day. That'll actually be the nicest decline of your advances. As you might in the future be dirt to someone instead of a friend. Friendships are wonderful things, don't discount them even if they aren't the romance you hoped for. You don't always get to pick your dreamgirl. You just might be some girl's dreamguy. Girlfriends help establish a network, an in road to girls that you might not have had a reason to talk to. Establish a distance in that friendship, don't be thought of as one of the girls... you want to be one of the guys. You should also not forget that lust only lasts a short time, while friendship and the love that comes with it will last a lifetime.
Also, you are juged by the company you keep. If you only have girlfriends and one guy friend others will think might think you're not a man's man, aka lady's man, aka womanizer, but they'll probably think you're a lovely human.
Edit: I wanted to add that at your age learning how to communicate with others without fear and develop and mange networks of friends and acquaintences will be something that will enrich the rest of your life. Dating is a huge factor in this and it provides a practice and proving ground.