You compose your draft on the basis of the prepared outline, but it will be quite natural if in the course of writing some points of the plan will change.
You may start writing the draft from the body, as composing a capturing introduction often stumbles the whole process. When the body of the essay is written, you will have a better idea how to captivate the audience with your introduction.
Once you are done with the research on the topic and the plan, do not hesitate to start putting your ideas onto paper. When you see your ideas in written form, you can judge them more objectively and writing one sentence will encourage the next one. You should not feel frustrated with a chaotic, illogical initial draft. Its purpose is to collect all the ideas together and serve as a basis for a final version.
After you have written the last word of your draft, take some time off and then come back to edit it. During editing you check on grammar and spelling, cut irrelevant information, purify, refine, and make amendments to your work.