This may not be the answer you’re expecting, but I believe fully valid for your question. One critical way to prepare for the academic load in any college-based officer-development program is to sharpen your time-management skills.
You’ll have to do well in academics amid many other obligations — military, athletic, other extracurriculars. Those who have strong time-management skills tend to do best. Smarts can only get you so far if you’re not adept at organizing yourself, setting priorities, being efficient, saying no, knowing when full effort is called for vs. moderate effort.
We all get 24 hours per day. We know that starting each day. So those who make the smartest use of them tend to be the most successful — both as cadets/mids and as officers.