When thinking about whether user interaction is good, it helps to keep in mind:
Does the user interaction resemble the user’s mental model of how things work.
We are constantly building and updating our mental models of how things should work. In the context of user interaction on mobile or desktop devices, these models are created by our previous experience with other apps and our real-world experience of how a similar task is performed.
We all have very similar mental models. We build it collectively by using the same tools such as Whatsapp, Google search, Amazon, Youtube, Facebook, etc. These shared experiences are what most users have come to expect from a user interaction. A good starting point would be to have a default sensibility of what that similar mental model is like.
If you have a prototype on hand, go over to another department and ask people such as the marketing or finance staff. Usually, asking 5 people would uncover the most severe usability issues.
This post is based on a chapter in the book: “User Interface Design For Programmers”. You can find the book at this Joel On Software (Article).
A user interface is well designed when the program behaves exactly how the user thought it would. - Joel Spolsky