I really liked this framework from Sean Ellis.
Make a huge list. Get everyone on your team involved.
Pick the best ideas and give them each a score of 1-10 in each of these three categories:
- Impact. How much of an impact would the test have it worked?
- Confidence. How confident are you that it will work?
- Ease. How easy will it be for you to test?
But curious to know if this is simplifying things too much? How do you prioritize which tests to run, how long do you run them, etc.