If you are studying for JLPT N1 then chances are that you
have already taken lower levels of the JLPT, or you have been studying Japanese
long enough to have some familiarity with the test. However, if you are like
me, and you jumped straight into N1 without taking the lower levels, the
following information may be helpful.
Master the 常用漢字. Without the kanji knowledge, you won't be able process any of the text, so don't even consider N1 until you can read them in your sleep. If you are a visual learner, this should be a cakewalk. More obscure kanji likely won't appear in the explicit kanji section, although even non-常用 kanji are fair game for the essays.
Vocabulary:
This is ultimately the most important part. It's obvious, but your performance on all parts of the test will be determined by how wide your vocabulary is. The JLPT has a predetermined vocab list, and all the words from N5-N1 are fair game for the vocab section. However, only knowing these words won't be nearly sufficient for getting through the essays. Some jargon will be defined in footnotes, but there are many academic and business terms that you will need to figure out that aren't in the vocabulary list. It's not unusual for uncommon meanings of words to be tested in the vocabulary section, and set phrases commonly appear in the essay and grammar sections, so I would recommend giving each word a thorough look over..
Grammar:
You will need to learn a huge amount of vocabulary for every point increase you would like to see on your overall N1 score. Assuming you haven't mastered it already, the quickest way to increase your score would be by refining your grammar skills. The N1 grammar isn't particularly difficult to begin with, and with a smaller pool of material for questions to be drawn from, small skill increases in this area will have a more noticeable effect. It's unfortunate that the number of grammar questions was reduced when the JLPT was revamped. It's true for lower levels of the JLPT also, but you should become pretty familiar with keigo. Not only with sentence construction, but also keigo specific vocabulary or noun+verb pairings (お年を召される as opposed to 年を取る). Questions may appear where you have to choose the correct noun to fill in the blank as opposed to the correct grammar construction.
Essays:
Getting better at the essay section isn't something that can be accomplished over night, but as vocabulary and grammar skill increases, so will reading comprehension. The best way I can suggest to study for the essay section is to read a lot, but you want to read things which are similar in nature to the essays that will appear on the exam. Academic journals are obviously a good choice, but the average person probably doesn't have good access to academic periodicals in Japanese. A surprising alternative is Japanese Wikipedia articles. Although the syntax often isn't as obfuscated as it is in N1 articles, a good portion of the N1 grammar will appear on Wikipedia, and you can read about things you are interested in. Then, your reading speed will increase, and ideally you will become more familiar with the style or writing, so when you open up the test booklet, you don't have to waste time trying to un-pry your jaw from the floor. Also, translating difficult written pieces into English can help because it forces you to be critical about the author's writing style and to think about why and what is being said (as opposed to just absorbing it and moving on).
Listening:
If you've lived in a foreign country for awhile, you probably already know how hard it is to get your listening skill up. It's not something you can just sit down and study for like vocab; it requires experience and progress is slow. I suppose it's similar to reading ability, except I think in this area it's harder to see when you're actually getting better. Anyway, listening for practice isn't going to be of any benefit unless it's directed and focused.
The Japanese used in the listening part is generally the kind of Japanese you would encounter on a daily basis in the real world, including things like political speeches and business meetings. Difficult words will appear in this section, but it's not as complex as the essays. The difficulty of the listening section is primarily that the questions are designed to be confusing. It's vital to listen to questions until the end; someone might say something that sounds like the answer, but then change their mind at the last second.
Unless you have ample time before the exam (i.e. months), I think you should just accept your listening level as it is and focus your energy on other sections. However, if you do have some room to increase your skill before the exam, here's one really useful website: http://news.tbs.co.jp/. It's a news website that includes an exact or nearly exact transcript for each video. There are a lot of ways you can study with this, and you have the transcript as an answer sheet.. Some ideas: make a summary and answer the big 5W1H, type up as much as you can verbatim, watch a video a couple times and try to say the Japanese simultaneously with the speaker (without looking at anything).
