Writing isn't just something you do in a sudden burst of activity when the essay deadline starts to loom - this last-minute approach usually produces poorly organized and incoherent essays. You need to develop a sense of writing as a process with a number of phases, only the last few of which involve setting pen to paper (or finger to keyboard).
Students typically panic about writing because they feel they've nothing to say. This sense of mental blankness (writer's block) is, paradoxically, caused by being aware of too many possible things you could say. If you avoid committing yourself to any particular approach, your mind is unable to form a coherent mental picture of the topic, so that it seems impossible to form a connected argument.
You can escape from this mental blankness by defining the problem, which means not just copying out a definition from a dictionary, but systematically thinking through what the question is asking you to do and developing writing strategies on the basis of the research you've already done.