The SAT is the single most important event in an American's life that they have
any control over. Simply going to college improves average salary by 50%, and
getting a good SAT score improves chances getting into a college.

I would say that the SAT is the most important part of a college application
because it _applies_ to every single college, where colleges usually have
different essay prompts.

Having read all of The Official SAT Study Guide except for the practice tests,
which I will do shortly, I have some advice for the SAT.

Practice test taking, particularly the SAT format. The book I got with some
past SAT tests was about $20.
https://collegereadiness.collegeboard.org/sample-questions/
has sample questions, too.

The format of the SAT is Reading, Math, Writing, (optional Essay I won't be
taking).

The reading test has passages and multiple choice questions that go along with it. Notable passages I came across were from Edith Wharton's Ethan Frome, which is a romance novel and an article from the huffington post. Neither of those things should be in anything official of any sort, much less a test that nearly all schoolchildren took in their respective years.

Outrage aside, the questions are dead simple, but in order to answer them in
time, there is a specific method people don't tell you.
1. Skim the questions. Remember what to read for.
2. Skim the passage for the general idea. Take note of potential answers.
3. Answer the first one or two questions that ask for a summary.
4. Go down the passage, answering questions. Questions are in the same order
as they appear in the passage.

Math is exactly the same as any math test I've ever taken.
It's all stuff that I'm a bit rusty on, so I'll practice lots.

Writing is much the same as reading, except instead of analyzing a
"well written" passage, you will be editing a poorly written one.
The study guide says "Pick the best answer," which you have to interpret as
if you were a stuck-up, sensitive, white soccer mom. You will only have an
average of 40 seconds per question, more or less, so think fast.
1. Read question and ALL answers.
2. Rule out incorrect grammar.
3. Pick the answer with the best "flow," reading it in its spot in the passage.

I hope you don't fail as badly as I will.

Edit 2017/11/15:
I got a 28 on my ACT using this method, which is an improvement from the 23 I
got last year.

Edit 2017/12/1:
I got a similar score on my SAT, with similar improvement.

High school GPA is just as important as SAT score.