Don't write "dang, you're hot!!" or "killer boobs!!" or some such.
The key in initial contact is to stand out and be original. A lot of PUAs/dating gurus say this, but in my experience it has worked. I've had many dialogues, meetings and at least responses by using that method.
If her profile says "I like to hike" or "I really like baseball" ask her "where have you hiked to?" or "You think the Red Sox will win the World Series soon?" Better still, make a joke out of her profile comments, in a ****y way. Once on OKCupid, a woman said she lives in Barcelona in Spain and it was one of her hobbies to see Barca FC. I sent an initial message saying "You like Barca? Oh, that's the one-man team with the Argentinian carrying everything? lol" She responded and was quite amused, and it went from there.
I guess by being a bit ****y/funny, it urges the woman to respond, if not out of thinking "ha! this guy has cheek lol... let's see what he's all about".