Since the essay portion is completely blind, how do I prepare for it?

The LNAT essay is not likely to be anything like an essay that you've written for any of your other subjects. You can't revise for it in the traditional sense. However, that does not mean that you cannot prepare for it. You will be presented with three essay questions, of which you choose to do one. Your choice is ultimately the most important few seconds of your essay time, so use it wisely. Up to the date of the exam, you should be keeping on top of current affairs - politics, business etc. so that, statistically, at least one of the three questions will be something you have an awareness of. Subscribe to a newspaper and take twenty minutes out of your day to read it. If you can bring in wide and relevant knowledge of goings-on, you will show your universities that you're a cut above the rest. The best way to prepare for the LNAT essay is to practice. Over and over - find online sample questions, write them in the 750 word limit. As you do so, you will figure out what method works best for you, what structure you can best fit into the constraints set by the test. If you figure this out, you will be saved valuable time in the test centre.Practice makes perfect, with the essay portion of the test especially so.