Technical writing has to involve a logical structure from problem to solution to evaluation.  But before you are at the stage of writing down all the details, it is often a useful exercise to write down just that logical structure.  Then, your mentor can see whether the ideas hold together.

As I have written elsewhere, the key concepts to describe are:

1. the problem;
2. that the related work does not address the problem or not well enough;
3. the proposed solution;
4. an evaluation that your solution improves on the problem beyond the related work. 
5. the results.

Writing in point form, it is easy to start delving into details.  If the point is to simply make sure that the argument is logical, this is a mistake.  Otherwise, replacing sections of the point form with details can be a useful, iterative approach to writing.