A major mistake that most people make during bar prep is failing to get started taking practice exams soon enough. This generally isn't much of an issue with the MBE, since the only way to really study for it is to do practice questions. They're short and quick, and therefore no one really seems to have issues with procrastination. Not to mention the answer is right there in the question. Sure, it can take quite a bit of skill to decipher which selection is the right answer sometimes, but it's there staring you in the face nonetheless.
Not so with the essays and the PT. The essays really seem to trip a lot of people up because there is a huge volume of material that could be tested on any given essay question. I believe it is the sheer magnitude of 'bar exam law' that intimidates students from attempting practice essays. The thinking being that you can't test your knowledge of a subject until you have fully learned the material. It's a logical argument, but bar exam prep simply doesn't operate under those regular rules of logic.
When preparing for the bar exam, it is IMPERATIVE that you begin to test your knowledge as soon as possible. This is for a number of reasons. One major reason is because you are going to have to be able to perform that exact task on the exam. Therefore it goes without saying that you need to be well-versed in performing that task long before you walk into the exam. The only way you can get really good at something is by doing it over and over and over again. The old adage holds true: practice makes perfect.
The second major reason you need to start taking practice essay (and PT) exams as soon as possible is this: it is a means to learning all that law. Don't think of practice essays as just a test of whether you know the law perfectly. See it as a way in which to learn any law which hasn't gotten cemented in your gray matter just yet. If you make yourself struggle through an essay, you will learn whatever legal principles are tested in that particular question. Intuitively you already know this to be true: if you simply quiz yourself with a flashcard you will not learn the rule as well as if you had to stand up in front of a class and explain the rule and its application. Taking a practice essay is essentially the same thing. It is you standing in front of the [imaginary] bar grader telling them what you know and how to apply that knowledge to the present legal question.
I think that law students (in particular) are so afraid of failure that they do not want to engage in any activity that they know will reveal any imperfection in their knowledge or performance. Most people who have become law students are used to always being right or excelling at any academic challenge presented. It is against their nature to engage in an activity or test of their knowledge unless they feel adequately prepared and in control of the outcome. That is a wonderful quality to have as a lawyer. And it is exactly what needs to happen when you walk into the bar exam. BUT, that is simply the wrong attitude to have regarding bar prep. Bar prep is precisely where you should engage in activities that will strengthen yourself for a strong bar exam performance. So it is okay if you find out during a practice exam that you don't know some legal rules, or can't figure out how to organize that cross-over question. That is why you're practicing now.
Suffice it to say, the earlier you get started doing this, the more you will have accomplished come the bar exam. And the more you do, the better prepared you will be. Don't wait. There is absolutely no reason you cannot start doing practice exams the very first week of bar prep. This goes for PT practice as well. Make Sunday your PT day - do 1 every Sunday.
To close, I'm going to let you in on a little secret: the first few practice exams you take are going to be the hardest, NO MATTER WHEN YOU TAKE THEM. That's right - it doesn't matter if you wait "until you feel ready" and when "you know enough law" (which, by the way, you NEVER will), or if you start on day 1 - the first few are always going to be a challenge. It is going to be a painful experience. So don't wait. It truly doesn't make it any easier.