Familiarity with the constructed response format is pretty critical. We’re not talking formal essays here, I’d recommend finding some videos/classes that cover the format, because getting competent at quickly formulating direct, specific answers to the question at hand is probably the biggest differentiator in the AM.
Once you get a feel for the format of a quality answer and the material, practice is key. Past AM exams are your friend, as is having an actual friend who can objectively grade your practice answers (it can be really hard to benchmark your own papers).