Who will be reading this essay? What is this essay for? Knowing your audience will help you decide the tone of your essay and help narrow down what goals you want to talk about. If, for example, the audience is a panel of academic administrators who are giving out a scholarship, then the tone of your essay should be formal and the goals that you focus on should center around what the scholarship will help you achieve. Conversely, if the essay is for a local newspaper then the form can be more relaxed; however the goals should still be narrowed down to what you think the readers will find important.
Though you may have a variety of goals that you plan to address in your essay, it is important to develop a main idea in your essay. Choose a overall goal that you hope to achieve, and then address several mini-goals within that context or organize your goals and find a way that they relate to each other. Lay out the main point in the first paragraph and use it as a reference point throughout the essay.
The best way to have your essay stand out is for it to contain unique information that is personal to your life. The "personal" aspect of the statement of purpose often gets lost in academic writing. Use appropriate, but unique, examples from your life when describing why you will be able to achieve your goals. Do not be afraid to think outside of the box when you list your goals. Have your essay reflect your personality while maintaining a professional quality.
Once you finish writing your essay, leave it alone for a day or two and then come back to it for proofreading. You will have a fresh mindset and it will be easier for you to see what needs to be edited. You may find parts that need to be edited out and other points that need more elaboration. Have your friends read over the essay as well; they may find typos or grammar errors.