Yes, this is an ad for coffee. But, stay with me here. If you want someone's attention, the video below is a perfect example of why you can't just walk up to people nowadays and say "hi".
This applies to the person who has the job you want someday, the author who inspires the hell out of you, or the cutie you see on your way to work — have something appropriate to offer, even if it's just a pertinent question. Oh, and try to be relaxed about it.