Why are players playing your application? Ask them questions such as Why did you do that?, Do you understand the rules or is it confusing?, or Did you expect that to happen?. Getting feedback at these crucial moments can let you know whether the game is being played and understood as it should be. Of course, you need to keep in mind what you want information about, as the preceding questions are very general. This is a good place to begin, but as the testing develops you will want to ask more specific questions, such as Did you feel more motivated when you received a badge? or Is it tedious having to select from a large array of options?.
While testers are interacting with your game, observe how they are doing it, just like in the following screenshot. Do they engage in a particular way that is not intended? This may demonstrate that you have some glitches in your experience that could even be exploited. For example, if...