1. Body language. Make sure you uncross any arms or legs, keep yourself open. Crossing your arms actually warns others not to approach you. Keep your head up and your posture as good as possible. You have to portray the image that you are friendly.
2. Smile. This one's probably the most obvious and helpful. People can tell when you're faking, but a fake smile is better than no smile. Just try. c:
3. When you talk to someone, compliment them within the first two minutes. Don't go overboard, but maybe just a nice comment about what they're wearing, their hair, or whatever they're doing. It makes them feel more comfortable with you, and more compelled to be your friend.
4. Don't be afraid to talk to someone next to you. I know, a lot of you are shy. I am too. But the more you make conversation, even if just about a class or the weather, the easier it'll be. Sit next to someone new at lunch or in class. It's ok to branch out, believe it or not.
5. Finally, don't be afraid to ask questions. People love to talk about themselves. It'll take the light off of you, and keep the other person intrigued. At the same time, don't ask too many, and make sure to listen intently and give feedback. It's no good for someone to talk to deaf ears.
These worked for me. That's all it took. In one week, I've made ten friends by just practicing this. I'm sure you will too.