How would I structure an essay on the theme of betrayal in Othello?

The most important part of writing an English essay is the plan, and yet it is the aspect most neglected during an exam. In order to structure this question, I would first brainstorm the key examples of betrayal within Othello. The first examples that come to mind would be Iago's betrayal of Othello, Othello's betrayal of Desdemona, Othello's ultimate betrayal to himself, Emilia's perceived betrayal of Iago and Desdemona's perceived betrayal of her father and family.
My next step would be to consider what links all these examples. For me, what links them all is the character of Iago. If he is not committing a betrayal, he is manipulating others to do so, or facing the turning tide as he himself is betrayed. From this, I would form a thesis statement to include as the final line of the introductory paragraph. This is the point you'll be proving throughout the essay, meaning it is an important part of the structure as a whole. It must be succinct and allow room for all the points you plan on making. For this particular essay, given the topic and examples, it could be something along the lines of 'betrayal is inextricably linked to the Machiavellian character Iago' or 'the theme of betrayal is wielded as a weapon by he who recognises its power.' It is then possible to divide your examples into three body paragraphs, such as how Iago manipulates others to betray, how Iago himself betrays and yet how Iago is himself betrayed. In the conclusion paragraph, I often then turn the question on its head, considering how, perhaps, what is important is Iago never betrays himself, despite his use of betrayal in others, announcing 'from this time forth I never will speak word', perhaps a demonstration of his strength of will as opposed to those he manipulates.
The trick is finding a running thread between all your examples that can form the spine of your essay. The rest will fall into place, especially when following a structure such as the PEEL paragraph (Point Evidence Explanation Link), which is something that can be easily taught. The hardest is finding a thesis statement that links to all the points you want to include that is still original enough to catch an examiner's eye. What is most important is a knowledge of the text itself and practice.