Copied from a recent message from a user:
 Hey!
I just got a few questions about the application process.
I go to a non-feeder school and has aspired to study in one of the many
prestigious colleges in USA, in particular either of HYP.
However, the process seems kinda of complicated, I'm not sure where to find out
which SAT subject tests to take for the 3 universities, because i presume they may have some prerequisite. 
Could you advise me on the process, and when i should take the test ( i have not studied at all at the moment).
I will be really grateful for any help.
Thanks Alot! 
1) For the subject tests, be careful about what you take. You usually need at least two subject tests for top schools; I think MIT might require three, but I'm not sure. I took three and I took them all on the same day. The sciences might require a little bit of extra study, but not too much (maybe try getting a revision book... personally I didn't use anything for physics, but I did UMEP). DO NOT DO MATH LEVEL 1. If you do specialist, math level two should be at about the right level. I just did methods but took the math level 2 anyway, and I was fine. Be very wary about the language tests, as those tend to be really really really hard... and stay away from the history subject tests, as the US has a different view on world history...
For the subject tests, you might want to take things which are relevant to what you want to study. For instance, if you want to do the sciences, definitely take math level two, as well as physics, chemistry or biology. It's also good to demonstrate that you're well rounded, so if you're strong in another language (I'm talking high 40s-50 in VCE), take the subject test. The literature subject test is also popular, but it's apparently quite hard. 
You can find practice questions on the college board website. 
Depending on how much of each subject you've already done, you might need to do a lot of preparation or none at all. You can buy practice books on eBay or find very dodgy practice questions on sparknotes. You need to have done the subject tests on or before the december of the year that you're applying (so if you're going into year 12, you want to have done them before december or in december next year - although when I was in year 12, you couldn't sit the SAT in Melbourne in december). You generally register about a month or two in advance for the test. You can also retake the tests, so take them when you feel comfortable, and if they're a complete disaster, you can always pay again and resit (although this isn't a good option financially and also doesn't look as good as taking it once and acing it).