As you begin the first draft, do not worry about crafting a captivating introduction. Many find writing the introduction the most challenging part of the essay process, and allow it to prevent them from starting. It is better to plunge directly into the body of your argument, with perhaps a two-sentence opening, simply summarizing your thesis. Once you know what you have said in the essay, it becomes easier to find an effective way of introducing it.
It is important to realize that writing is a way of thinking. Do not feel that you have to have all of your thoughts fully organized in your head before putting fingers to keyboard. A written work is not an Athena and will not leap fully formed from your brain to the page. It is a carefully prepared and heavily revised simulation of rational thought that usually begins as a series of poorly expressed and disconnected ideas.
Once you have done your research and planned your outline, the best way to think about your essay is to write it. Seeing your thoughts written down allows you to regard them critically and objectively, and putting one sentence down will inspire another one. There is no need to feel disappointed with a messy, even incoherent first draft. The purpose of the initial draft is to produce raw material, not to dazzle the critics with your finely-shaped prose. Having something on paper gives you something to work with.