I'm 20 and have been single for a few months now..... oh dear this whole thread sounds like an AA meeting.
nether the less I've never had problems talking to girls and (apparently) I'm quite good looking, I also am very into sports so am in pretty good shape and at 6ft am usually seen as a decent height etc.
so my advice from someone who clearly knows everything (sarcasm) is..... neither I nor anyone else on this thread giving out the advice has some kind of lucky genetic jackpot that means we just click with the opposite sex. most of the time girls are just as unsure and shy about these things as you are.
at least 90% of this is just confidence. in my experience the friend zone can usually be avoided if you act early enough, in a very casual way try chatting with a bit of casual flirting. also ask your friends, I'm personally very neurotic and over think a lot of what others say, if a girl makes a certain comment to me I will spend ages analyzing if that was her flirting or being disinterested etc. a good friend will usually say 'mate, just go for it shes clearly not ignoring you and shes a nice person, if you get shot down then who cares?'
at this point you man up, finish your drink and approach her. aside from a very few, girls arent going to be horrible to you if they arent interested. they will most likely say 'yes' or look a bit uncomfortable and mumble something along the lines of 'sorry, no' at this point she is usually as embarrassed as you and not being vindictive and superior. simply say 'hey no problem, hope we can still be friends tho' to which she will (almost surely)jump at the chance to end this awkward conversation and agree to remain friends.
Ive been on dates with a couple of girls that never really took off, most of the time we have remained friends afterward and while it may be a little awkward for a few days it really will go away if you just push through it and don't shy away from them.... tho do this casually in a group, i mean don't avoid her but you don't have to stalk her just to show that your ok.
what you shouldn't do is avoid them for so long that you can then no longer even talk to each other in case you end up being forced together through some deus ex machina event (this happened to me last term, my new partner for a course happened to be the best friend of someone I had a thing with and never spoke to afterward, bad times)
anyway rant over, just go for it, most of the time it will work and if it doesn't then who cares? get over your fear and maybe you will surprise yourself