For school assignments like this, I like to print out the instructions and underline each individual part. I ask myself what the purpose of this paper is, what they are trying to get me to do and/or think about (which they usually very clearly state; sometimes it just takes slowing down and breaking it down to get a grasp on it). Then that usually gets the juices flowing enough to write something, even an outline or just ideas of what to talk about. If not, I will write down each individual part of the instructions, with each one followed by my thoughts, ideas, questions to ask or look up, etc.
I also have read the wonderful book A Mind for Numbers a few times, which is about how to learn math and science. But it also goes into procrastination and how to defeat it (which I personally think of this kind of mental block as a form of procrastination). One of the things that stuck with me and that I remind myself of, is that it’s normal to feel uncomfortable when you first sit down to work. Our brains actually perceive this mental anxiety over the task as physical pain, but studies have shown that the task itself is never as painful once you get started.
I hope these tips/things to think about are helpful!