How do you decide what features should be free for a software side project?

I’m building a Chrome extension called TaskQueue to help with task management and focused work sessions. Right now, I’m planning the premium version and trying to decide what features to keep free versus premium.

I want the free version to feel valuable, but I also need the premium to stand out. Have you ever struggled with this? How did you make the call?

If you’re interested, here’s the link to TaskQueue: TaskQueue on the Chrome Web Store. I’d love to hear your thoughts and maybe share some of what I’m working on!