Is there any chance you can give a bit more information?
Based on what you have said I would try to talk to some of your end users. There are numerous JS plugins that allow your users to give feedback, chat to you in real time, track mouse movements.
In addition you can email your list of subscribers with a personable and friendly email asking for help. Maybe something like this:
>>>
Hi Dom
It is James here from coolwebsite.com. Just seen that you have been a member for 7 days, and wondered what your experience has been so far? Anything I can do to improve?
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The general point is gather information from your user base. Work out who they are, where they hang out. You may figure out better ways to market your site based on this to get better conversion rates and more subscribers.
Also check that the free version is positioned right so there is incentive to upgrade. Patio11 wrote a good blog post about this topic once - I can't remember the url but somewhere in here: http://www.kalzumeus.com/blog/