It's all about tatics. each guy have their own.
Usually, I follow the Path of the Uninterested Ninja.
Well, it's not a direct answer to your question, but maybe it helps a little:
In my view, it depends on how other guys behave with you. If you are a girl that has a lot of guys around you, all clearly interested in you (and it clear that you know that), I show no interest. I will not compete directly like the scum. It's all about catch the attention and have something different. When we talk, of course I'll be nice, but not too nice like the others. I think that looking deeply in the eyes (in tactical moments, not always like a psycho) helps.
If you don't have fans all around you all the time, the best - I belive, is a similar aproach, but I can be nicer, showing a little more that I enjoy beeing with the girl, but never let her be certain of nothing, but in the right moment, when you see an open spot, I "attack" (stepping really closer to her, asking her out, kissing her, depends on the situation and progress).
It's very rare I just ask a girl out with no "warning". I am shy, so It's very hard to me to do it.
Usually I just do it when I belive that surprise factor will be effective.
Oh, I am not so cold to do all that stuff with a girl that I am liking without having some problems, be silly or wihout have inner struggles, but I try keep that tracks in mind, because I observed more success "using" those ways. That's me nowadays, at least.