Check out various articles online about heuristic evaluations (https://en.m.wikipedia.org/wiki/Heuristic_evaluation - as a starting point). They will give you checklists that people use for general purpose assessments.

As a rule of thumbs, it’s a good idea to conduct a heuristic evaluation as an initial assessment of usability, make changes as needed, and then conduct an actual usability test to ensure you hit on the points you need and your users can accomplish key tasks in your app...