How do you make sure your essay does not lose focus?

Continually link back to the question itself, and reference/cite the question at the start and end of each paragraph, and/or wherever else you see fit. This heightens your analysis and response through a continued focus on the question so that you avoid straying from your argument. So, neither you or the examiner is confused because your thoughts are organised in an essay format instead of your essay showcasing a confused and unorganised thought process. Therefore, planning is also essential to let you structure your thoughts and ideas.