First things: if you're not convinced of the importance of cutting churn, check out our churn calculator, which shows you the impact on your revenue of cutting your churn rate: https://memberscore.io/churn-calculator
There are a few approaches to reducing churn; all of them are valid, and can be applied in parallel.
Catch members with declining engagement.
The premise here is simple: when members become less engaged with your offering (less frequent site visits, not posting in discussion forums, not completing courses/videos, etc.), you reach out and help them re-engage so they don't cancel.
Of course, measuring engagement is the tricky part. But thankfully, MemberScore can handle all of that for you.
Improve the membership experience.
The goal here is to make your offering so good that fewer people cancel. A great way to gain some insight into what's causing people to cancel: an automated (or personal, if you're low volume) "exit survey". When someone cancels, send them an email asking them to fill out a very short "why'd you cancel?" survey. This could literally say "why did you cancel?". You could also use "what could we do better?", "how could we improve things?", etc.
Increase the appeal of longer-term subscriptions (and pitch them).
Getting someone to commit to an annual subscription can be a fantastic way to reduce churn. There are two factors here. First, it reduces the cognitive load of seeing a charge on their credit card each month. Second, it gives you a full year to prove the value of the membership, so when they do come up for renewal, you've got a better chance of them not canceling.
A great way to get people switched over to an annual plan (assuming they joined with a monthly subscription) is to send an email (or multiple) at their 2 month mark, with an offer to switch to an annual plan at either 83.3% of their monthly cost x12 (in other words, 12 months for the price of 10), or for 80% of their monthly cost (which lets you promote "20% off").
Applying all three of these techniques will make a significant impact on your churn rate. But, that might be overwhelming; if you need to, just start with one (pick whichever is easiest for you right now).
And of course, remember that MemberScore can take a lot of this off your plate, and free up more of your time to work on your business and grow your community.