Beta groups are a great way to test features and get feedback prior to shipping them. Again, it’s probably best to target specific segments of users.
To solicit users, you can use a dismissible in-app banner or pop-up. You could email a targeted set of customers. You can also announce it on social media, on your blog, your podcast, or your newsletter. Users who consume these channels tend to be a good fit.
It’s helpful. If you can have a centralized staging server where beta users can preview new features.
It’s also helpful to have a slack channel or a blog where you can communicate with beta users and they can share feedback with you.
Once you have everything set up, remember to update your internal processes, to leverage this asset. As a beta list is pretty worthless if you’re never going to use it.