By and large, EVERYONE prefers the same thing: a friendly direct approach that expresses interest, without desperation.
The unfortunate truth is, in most rooms, it's too easy for a guy to assume a woman is smiling at someone else, or perhaps smiling at something she finds "funny" in a non-complimentary way. In fact, most of the men I've worked with have, at one point or another, been mis-cued: they thought they were being smiled at, when the woman was actually looking over their shoulder at someone else.
I'd say if you're interested, you've got nothing to lose by approaching a man you're interested in – except perhaps another dateless Saturday night. 😉