Is it ok to go up tp a girl I like and just say hi?

Right, there's a girl I like that is in two of my cles. English, and Science. It is the year 11 leavers day tommorow, but we're going to the same place for A-Levels, so all is not lost. Is it really ok to just go up to her and say 'hello?' I mean, wouldn't it be a bit weird? We havn't spoken before and I desperately want to make contact, I just don't know how. Cheers.