The goal is to detect usability issues. Your features should have user stories associated to them, come up with few scenarios around these (e.g. book a flight,

The goal is to detect usability issues. Your features should have user stories associated to them, come up with few scenarios around these (e.g. book a flight, cancel your flight from the landing page...). Then test your scenarios with multiple users/personas. This will allow you to detect UX/usabilities issues, and prioritize update based on how critical the issue is.