AP English Language and Composition is often taken for granted by strong English speakers and is then one of the harder exams to score well on.
What it is about
Non fiction: speeches, essays, letters, journalism. The question is not what the text says but how it works on the reader.
Who is speaking, to whom, in what situation, with what choices, and to what effect. That is the whole subject.
Three essays
Synthesis, where several sources are given and an argument must be built from them. Rhetorical analysis, where one passage is examined for how it persuades. Argument, where a position is defended without any sources.
All three are written in one session. Time management matters at least as much as writing ability, and running out of time is the most common way marks are lost.
The most common mistake
Listing devices. Naming metaphor, anaphora and repetition earns nothing on its own.
What earns marks is the effect: what the choice does to the reader and how it serves the writer's purpose. A device named without an effect is a wasted sentence.
For students whose first language is not English
The difficulty here is not vocabulary. It is producing a structured argument in English under time pressure, which is a separate skill from reading comprehension.
Students in international schools often read at a high level and still find this exam demanding for exactly this reason.
How to prepare
Write under timed conditions and read your writing against the published scoring guidance. The College Board publishes scored student samples, and comparing your own essay with them is more useful than any amount of reading about technique.