I'm currently experimenting with a minimal opt-in that leads to a short survey. Though the inverse (like @Blair Wadman55 mentioned) works great too, though adds a bit of upfront friction while allowing for personalized opt-in forms.
Landing page: https://rightmessage.com/free-course/70
Confirmation page w/ survey: https://rightmessage.com/course-ty/55
Getting some fantastic segmentation data, which is being used to personalize the actual email course based on who they are and what they need.