How to catch girls attention on first glance?

It saddens me that I get overlooked by girls most of the time. I've had a few girls over the past year anyway, but in times when I've been single, I've often tried to get girl's glances but have never been successful. I've done the whole looking over thing, quick glances and that, but I never get any response... on the train earlier, for example, was this smashing girl, did all the glancing and stuff but she wasn't interested at all. I wouldn't say I was particularly bad looking, and as I say I have had girls, but stuff like this knocks my confidence... any hints?