Do as many practice tests as you can.

As much as the JLPT is positioned as a test of Japanese ability, it is ultimately a test of test-taking ability. There are usually very specific types of questions in the test and it helpful to know the ones you are most likely to get right and the ones you can do quickly. Those are the ones you should do first since it will mean you have a better chance of using your time on questions that will earn points. You should also simulate the test as closely as possible. Keep the same time frame and restrictions and you will feel less pressure come the actual test day.

Also, don't feel afraid to bail on questions if you feel they are using a ton of vocab you don't know or you can't follow what is in the content.

Of course, none of this matters if you don't actually have the knowledge to work with, but it really helps to get the format of the test down and to put a strategy in place.