How to ensure your Essay makes sense under timed conditions.

Firstly, Keep it simple. This might seem counter-intuative, surely you want to wow the marker with your mastery of the finer points of the english language? The fact is though if the examiner can't understand what you're point at first glance they probably never will. Try and remember that your examiner will have read hundreds of essays just like yours, and it's much more likely to stand out if it's written in simple, accesible language they don't need a thesaraus to make sense of, than if it's a poorly constructed string of flowery adjectives. It's better to use that fifth 'On the other hand' than waste time trying to make it 'sound better' and ending up with something that's more difficult to read than what you orginally wrote.
Next, Make a plan and Stick to it. Start by picking examples from the text that relate to the question, For example if you were asked “Shakespeare clearly leaves us with the uncomfortable sense that authority is always insecure.” Examine this view of The Tempest. You would need times authority is exerted in the Tempest, try breaking it down into catagories like, familial, social, and governing authority. Then pick a side, there's no right or wrong answer so it doesn't really matter which one you choose as long as you can argue it affectivley. Once you've done that you can decide how if your examples prove or disporve your argument and how your going to link them to context, literary devices, crtical opinions etc. and then finally decide what order you're going to discuss everything in. I'd recomend starting by agreeing with the question, but the main thing is to outline the order in your introduction and then stick to it.
Finally, Start with a question. It can be difficult to construct an Introduction and Conclusion, and can feel especially repetative in a shorter essay. By ending your introduction by asking a question you then set up an answer to base your conclusion around. Sticking with the previous example this could be something like "Although authority fluctuates constatnly in the Tempest, can it really be said that it is always presented as insecure?" This provides your essay with clear structure that will make it easier to follow and therefore, easier to award marks to.