Update your site with quality content. Keep the users engaged as much as possible. When they lose interest there are more likely to bounce. Do you do email marketing?
Also consider offering discounts (if you're not already) for subs. Think of 34.99 as a one-time month access and 29.99 recurring or something along those lines. Work on creating value with what you have to offer. For the most part, this is trial and error and you will want to try out a couple of different variations to see what performs the best.
A/B testing; Consider creating separate join pages that show different subs/pricing. Then send traffic to these joins to see how they convert. Be careful here though... You don't want to create a package that is considerably less on one test. If the user finds the other price point they are more likely to make a chargeback since they didn't receive the best possible price.
