Imagining a nagging little voice inside your head asking the question "So what?" after every sentence or paragraph you write can be an effective way of reminding yourself that your essay needs to address the expectations of its imagined audience. The "So what?" question encourages you to explain your goals through signposting and relate the essay to the rhetorical situation in which it's placed.
If you find the "So what?" question hard to answer at any point in your essay, this may be a sign that you are writing in an inappropriately writer-orientated way - after all, if you can't explain the purpose of what you're writing, you can hardly expect your reader to know what it is. Asking if your reader is in a position to answer the "So what?" question at various points in your argument can also be a good way to improve the effectiveness of your writing when you start to review your essay.