I'm working with several Master's Degree students currently---some in Architectural Engineering and some in American Studies. I'm frequently the 3rd or 4th member on a student's committee, so I have the luxury of staying out of 'the weeds' and looking at these projects from a big-picture point of view. Here's my approach to Master's theses as a faculty advisor. I think this is probably useful for students in a variety of disciplines.
First I look for Clarity of Purpose and Significance. What is the Big Question the project will address? In other words, to the student, why are you doing what you're doing? You should be able to answer this very clearly. Is your subject important and will your contribution be meaningful? Are you sure your Big Question hasn't been asked & answered before? Students who struggle with these need some good guidance, or the project is in trouble. If it's a small question, let's make it Big.
Second, I want to know about Approach. You must have a specific plan for answering your Big Question. (And you shouldn't know the answers in advance.) Do you have the right tools to get reliable data? Are you sure your assumptions are valid? Are you aware of previous similar work that you're building upon? Are you going to be able to reach significant conclusions and speak with authority?
Be aware of whether you're using established methods of your discipline, or if you're innovating. You probably need a compelling reason to innovate. Ideally, in the end, you will have something like a chemistry experiment (even if it's a Humanities project), where someone else using the same procedure or sources would find similar results and reach similar conclusions.
Third, I ask what could go wrong. You might find a lot of evidence contradicting your hypothesis. The data might be messy or inconclusive. What will you do if you can't answer your Big Question with confidence, or if the conclusions are simply dull?
Finally, I tell students that writing is easy if you're thinking clearly and have a lot to say, but it's difficult otherwise. Give special care to distinguishing between facts and interpretations. Don't try to write 'like an academic' because this usually means being purposely unclear. Short declarative sentences are good.