Writing strategies are ways of preventing yourself from developing writer's block, a condition in which you feel paralyzed because there are too many possibilities, and which is often the result of waiting for inspiration to strike, instead of taking a systematic approach to the task of writing.
One of the most effective ways of preventing writer's block is to think of your work on the essay as moving through a series of distinct phases, rather than expecting everything to come together all at once. Restricting yourself to working on one aspect of the essay at a time may seem artificial but, paradoxically, it will enable you to think less rigidly by stimulating your ideas.
Writing things down (perhaps by keeping an ongoing writer's notebook) can also help to break the logjam of ideas represented by writer's block, since every idea you have to remember is taking up valuable mental capacity which could be used to find solutions to your essay-writing problems (an approach which underlies various forms of time-management). Visual aids to planning, such as mindmapping, can play an important role here, but sometimes it is enough just to abandon the unrealistic assumption what you write has to be perfect, since it is much better to have a draft which you know needs some revision than a "perfect" unwritten essay - taken to an extreme, this strategy underlies the technique of freewriting, which is designed to help those who suffer from severe writer's block.
Finding several different ways of rephrasing the points you want to make can also be a useful strategy in combatting the false feeling of having nothing to say which underlies writer's block, since this will suggest various ways of developing your arguments into paragraphs. A large proportion of any successful piece of academic writing consists of different ways of putting the same thing, so you will find the ability to restate a point while varying the expression a highly useful skill to cultivate.