Before you read this, you don't have to approach scary good looking chicks to do this, not yet anyway
In my college class there is this ultra quiet boy who never speaks and I get the same bus as him home. I never spoke to him because he just seems unapproachable, always has a miserable face etc. However after starting a conversation at the bus top i realised that it was no different from approaching a girl.
I just asked him about the lesson and joked about the teachers. This guy wasn't as miserable as he looks and was actually open to a conversation.
This applies to girls aswell. Don't prejudge them before you know them. I know we all do it and think we can tell whether a girl will be nice or a total bitch before we even approach her. You'll find that you'll be proving yourself wrong a lot of the time.
I've seen girls standing alone looking like the biggest bitch on the planet waiting for her bus but as soon as I said "Hey" that bitch inside her (well what I thought was there) was gone and had a great smile on her face ready to have a bit of small talk
Anyway the point of my post is that if you are finding it extremely difficult to approach girls, approach guys. This will help you gain confidence and in time you will be able to approach girls.
You can just ask the guys for the time or something, an opening line that you may use on a girl.
After approaching the so called miserable guy, I gained a lot of confidence from that and I can approach people.
However, act as soon as possible as the more time you spend pondering about what to do, the more likely you'll convince yourself out of the approach.