the best way to approach girls is.. CAUTIOUSLY! hahaha...
but seriously.. you have to get really good at figuring out what you think her feelings towards you may be first! before you say anything! see... if i'm into a guy and would prefer if he would say something to me rather than try to steal glances, i'll smile at him, smirk at him, do whatever to seem interested when he catches my eye! he could probably say almost anything goofy, silly, innocent or sweet and get away with it... however! if a guy is 'checking me out' and i'm not interested, i'll either avoid him like the plague, or straight up give him a sh!t look when he looks at me... it would not be good of him to say anything to me, because it'd just end up in rejection...
see what i'm sayin? i guess the best thing to do is try to catch her eye, see how she looks at you, and decide if you'd like to say something... if you do end up speaking, keep it cute, not too forward or 'romantic', try not to try too hard.. even if you come off as kinda shy, that's okay! if you seem a little shy, it might even make her feel more comfortable, ya know?
okay.. i'm done confusing people!