The key to just going for it is having absolute disregard for what other people think or say. Don't give a fck. You live your life for yourself, not the other people around you. The only person you ever have to answer to is yourself, and I'd hate knowing that I wussed out and lacked the balls to go through with what I wanted because of others much more than caring about those people staring at and judging me. Practice so that this becomes a gut reaction. As someone who used to be one of the biggest thinkers you'll come across, I have to tell you: DON'T let your brain stop you. It makes you over-think it, build it up and make it into such a big deal that you'll get way too nervous and blow any chance you had to begin with. It's a self-fulfilling prophecy. Things you need to approach:
1. Positive, happy mindset that shows you feel good about yourself - confident but relaxed body language, the ability to smile and laugh
2. Some observational skills to break the ice
3. Stop thinking
Talk to everyone you can, not just girls you see. It's amazing how many more people say hi first when you stand up straight, pull your shoulders back, look them in the eyes and smile. Do this as a natural reflex that you do for yourself, based on trying to become the person you want to be. Don't let others dictate what you can and can't do.