the lust for power,
Okay, so this is the central idea of your essay, right? If you need an introduction and the conclusion developed, it means that you need your main idea developed. So, what is your unique idea about the theme of 'lust for power' used by Shakespeare? To write a great essay, you have to have a great idea. Is not a mechanical process of improving one part and then another part; you actually have to have an idea worth mentioning before you can try to express it in an eloquent essay.
When you do have a great, unique idea, it sometimes becomes very easy to structure your introduction in your conclusion in a good way. The goal is always to help people share and understand the idea that motivated you to write in the first place. So, now, you have done this much work and the concepts are fresh in your mind. I wonder what you will find when you review it again and ask yourself about the main idea that is worth writing about. Your own mind produces important ideas in response to the way Shakespeare portrays the corrupting influence of power, and it is your own reaction to this, based on your own knowledge and experiences, that will make your essay great.
Figure out your own main idea, and write a few sentences about it for the introduction paragraph in the conclusion paragraph. At this point in your process, it is probably best to use the introduction and the conclusion to explain your main idea in two different ways to help the reader understand.
:-)