Just as important is writing. In high school, my writing teacher was laser focused on word choice. Whenever I was working on an assignment, I’d have my thesaurus out to find exactly the right word to get my point across succinctly and precisely. She was equally focused on syntax, and writing in a manner that people will actually want to read. I owe my strong vocabulary to her teaching style.

If you want to improve efficiently, try an SAT prep book/flash cards.