If you have adequately prepared before and during the exam, writing the essay portion of your law school exam or bar exam will be the easy part.
Before the exam you prepared by perfecting your writing skills and becoming familiar with the IRAC method. During the exam you prepared by by reading the question several times over and outlining the issues by taking notes. Due to your preparation and outlines, you should now have a good idea of what your answer is going to look like and now is the time to put your legal analysis into words.
But now is not the time to become complacent. You still need to efficiently and accurately place the facts, issues, rules, and application into a readable format for the examiner, so that your conclusion is sound and supported.
Begin The Essay With an Introduction / Umbrella Statement
Start your essay with a brief outline of your argument, briefly mentioning all of the main issues, rules, and the likely court holdings. This brief outline is useful for several reasons.
First, providing this outline or "umbrella statement" is useful for the reader in any situation, but especially so on a timed exam where your logic and writing might become a little disorganized. Ensuring that your logic is organized and easy to decipher can only help you on such an exam.
Second, an outline of your answer can also provide points that you might lose otherwise. If for some reason you ran out of time before finishing the entire essay, having the outline shows the examiner that you understand the issues and rules, and could gain you some points.
Finally, after outlining your notes while reading your question, this is your last chance to refine that outline without making major edits to the essay. If you spot a flaw in logic here, all you have to do is change a sentence or two, rather than multiple paragraphs.
Organize Your Issues
Although you have had the IRAC method drilled into your head by now, you should not let that strict structure interfere with readability. If you have two similar issues, such as assault and battery, you can save a lot of time discussing these two issues simultaneously in one IRAC.
Additionally, especially on a timed exam, I always found it efficient to not write an IRAC's in the traditional fashion. Instead, I would simply write one application section without defined Issue and Rule sections. This works because a good application section is going to already mention each fact, rule and issue in depth, thus there is no reason to waste time repeating these times in their own section. A Simple Example:
Relevant Facts:
"John Doe [D] is charged with battery because he told Plaintiff [P] that he was going to fight him, then struck P in the mouth with his fist. D claims that he did not intend to hit P, and was just fooling around."
Relevant Rules:
According to State Law X, a battery occurs when a person intentionally causes unwanted contact with another.
According to Case X v. X, intent can be established if a threat of contact immediately precedes the unwanted contact.
According to Case W v. W, intent was not established when a man made contact with another man when he tripped while throwing a ball during a game.
Your Application (Issues + Facts + Rules = Conclusion)
The Defendant (D) will likely be convicted of battery. In order to be convicted of battery, state law X requires two elements be met: (1) that unwanted contact be made with another person, and (2) that contact be intentional.
According to the facts, it is uncontested that element 1 has been met. D made contact with P, which P asserts was unwanted. The facts do not clarify whether element 2 (intent) has been met though.
According to Case X v. X, D's intent can be ascertained by the fact that he made a threat of contact by stating "I'm going to fight you" before the contact occurred. This by itself would likely establish that both elements have been met, but Case W v. W shows that intent can be disproved if the contact was an accident.
In this situation, though, D's statement of intent to make contact will likely outweigh his contradictory and unsupported claim that the contact was accidental. Because of this, it is more likely that either a jury or a judge would find that both elements of battery have been met, and thus convict D of battery.
In Conclusion
As you can see above, you can make very logical arguments efficiently if you focus on writing efficiently and not repeating elements unnecessarily. You will need this efficiency because you will have to write a similar application section for each and every issue within the essay answer.
Having practiced this system or something similar, you will consistently produce well written and accurate answers and will be able to remain calm due to your preparation, where others might stress out and produce gibberish.