The cost for you is marginal or non-existent, and you get an excellent referral system.
When you sell a membership, give the new member a bonus membership (one, three or even more months) he can gift to anyone he thinks might find it useful. You can test it as a surprise after they already joined, or as another incentive to join.
Continuity programs give you stable and predictable income. This might help convince people to join.
Offer parts of what you provide in your continuity program (webinar, article, one-day forum access) for non-members for a one-time access fee. You should price the single access fee to make your monthly fee seem very attractive. So if your monthly fee is $79, you might want to offer a single access for a one-time webinar (that you would get for free weekly as a member) at $49.
Have a better audience for your website.
A website that shows no content unless you are logged in as a member. Membership is free, but you have to register. No functionality or content are given without registration. It’s a secret “club” for members only.
There are many benefits to being a member instead of buying. Some are personal access, no substantial upfront cost, always updated, quit anytime, etc. Having a members club is also beneficial for other reasons. For example stable income, attentive audience, etc. there is, however, one problematic facet to having one: you need to keep members interested so they won’t leave.
Build a membership plan that has only one component: you. Give the group access to you in the form of a weekly or monthly interactive (online or offline) group meeting, where you talk a little about your relevant experiences of the past week or month, and then anyone can ask questions, and you answer them. You should also close the meeting with a cliffhanger for the next one, and deliver the one you promised in the previous session. That’s it, nothing else. No Extra content, no new training, etc. just a periodic access to you and your brain.
Whether you want them to opt-in to your email list, or a continuity program, a higher and more committed opt-in rate is desirable.
Don’t use forced continuity (lots of refunds, complaints, payment processors don’t like it, etc.), or opt out. In both cases, you have one option that is checked. This is not as strong because it is a passive decision by the customer, and he is not making any real commitment to this choice (and he will opt out quite quickly.) Instead, give him two options to choose from. By making him “declare” his choice, he will have a higher degree of commitment. To further enhance this, also show him what he’ll lose by making the wrong choice, for instance: “Yes I need continuous help and today I will get the monthly membership for 30% less” and “No I never need any help, and I don’t mind losing the special 30% discount price and paying 50% more when I do need it and want to join.”