Do 30-day trials and put a reminder in your calendar to cancel with the URL to do so. Make this a habit. Yes, subscriptions are a dark pattern but the minimal amount of effort to avoid being charged in some circumstances (not gyms) seems like a small thing. That said, the world would indeed be a better place if businesses didn't charge you for service they weren't providing. Although you might model these monthly subscriptions as "insurance premiums" to save the 5 minute sign-up time the next time you want to watch something.
What I do is canceling the trial immediately after subscribing for it. Most services will let you finish the trial period and you won't risk forgetting to cancel it and paying for another billing cycle.
