No, you can’t really study. Arrive early so you don’t feel rushed and flustered. Get a good night’s sleep.
There are two tests. One is very brief. If you pass either one, you will qualify. You will not be given an “IQ number”; Mensa doesn’t do that anymore. You will simply be notified by mail whether you have passed. The proctor cannot tell you that; he or she is there to facilitate the test.
Don’t get hung up on any one question. If you don’t see the answer right away, go on. Then go back and make a second pass. It’s far better to get to the end of the test and have left some blank than to find yourself two-thirds done when time is called. If you have no idea on some, guess rather than leaving them blank.
If you pass, pay your dues and join! You’ll meet great people. And some jerks.