Planning planning planning combined with really knowing how to study efficiently. You have to be on top of every homework assignment, GR (test), paper and project and know exactly when they are going to pile up on you. For me that meant at the start of every semester, laying out the due dates from all my classes on a full paper sized calendar. I color coded based on whether it was HW/Test/project/paper, so at a glance I could see where the rough spots were. Often doing well means that every time you see daylight in your academic calendar, you pack that with homework to get ahead. Depending on the sport/team, you also often will have tutors that travel with the team. Smaller teams have to choose what tutor to bring, but generally that can be worked out with the coach. I was a math/physics double major and a tennis IC. I had a major math test I was struggling to prepare for that coincided with a 5 day trip to a tournament. We were going to bring a physics tutor, but since I could tutor physics, we ended up bringing a math tutor for me instead.
I also have some fun memories of getting up at the crack of dawn before the matches started at a tournament to take a history test because it had to be done the same day as the cadets at USAFA. I think there were 3 of us in the class so that's what we got to do while our teammates slept in.
The key is staying on top of it and knowing when you need to ask for help. My roommate senior year is now in the World Class Athlete Program (WCAP), but at USAFA she was on the track team. There were many late nights where I stayed up to help get her through her astronautical engineering homework, but she was one of the most diligent students at USAFA. Constantly studying and training for her sport.