You don't say how good their English is, so I will put it on the same level as Japanese teens I have taught.
You also didn't say anything about how often you are supposed to teach them, or how many lessons you have until the exam.
For the preparation they need, you should teach them how to form proper paragraphs (topic sentence and support sentences), which means brainstorming topics and then going to outlines before actually writing. See how well they do this in long periods, then shorten them up, because they may not have time during an SAT!
Teach them structures to use to compare things. Not just X is bigger than Y. Contrast, too.
Teach them how to interpret graphs and to describe the data.
Teach them how to use time markers (simple ones like first, second, third, and more complex ones like "when I was 2 years old", "in the days before 911", and so on).
Teach them how to use cause and effect to describe things. Sometimes cause is written first in a sentence, but sometimes it is written last, so the verbs are different. X causes Y, vs. Y is caused by X.
Push them for writing fast, but only 50 words at first, then 150, then 250. If they are anything like Japanese teens, they will have horrible grammar, but even more horrible organizational skills.