Try popping into the chatroom at night time if you want a great way to break the ice.
As far as I know, there are also two types of PM, one through the ad and one off the girls profile. I have never received a reply to one through the ad but 99% of any pm's through the profile were replied to. The fact that they have a profile in additon to their ad (a lot of girls don't) is a good sign that they are reasonably active on the site.
Always check for lipstick or makeup transfer before you leave the apartment