The one thing I have learnt over the years is there is nothing worse than walking up to a girl and looking nervous. The nervous energy just makes them feels nervous and in turn makes the whole atmosphere awkward.

Tip: Even if you are nervous, put on a persona, imagine you are a super confident guy, or if that's difficult, vision someone who you admire that is confident and pretend to be him.

Stick your chest out, keep your head held high and when you approach, smile and say hi.

Takes some practice for soon you'll see even the smallest change can make the girl's reaction much more positive. Don't be suprised if she smiles back. (it means it's working!)

Good luck guys.