In brief - the emails most likely to get a reply from women talk politely about the woman's individual profile or post ('You mention...', 'I notice that...', 'I'm curious what...') as do self-deprecating lines ('I apologise...', 'awkward...', 'sorry...') while pick-up lines get a negative response ('sexy', 'hot', even 'you're pretty').
It's kind of obvious really, and I'm sure the gents on my f-list know this kind of thing instinctively, without even trying. Just talk to women like they were regular folks.