Here is what worked for me as a Chemical Engineering major - I adopted these practices after struggling my first semester.
1. Be realistic with how much you can handle - I only took 12 to 15 hours each semester one exception. This allowed me to get mostly A's with some B's while traveling in both XC, Indoor Track, and Outdoor Track.
2. Set apart specific times for studying and include breaks - I planned for 1 hour of dedicated study per course per day with a 15-minute break between each. Get somewhere quiet, turn off your phone, and work on studying.
3. Create study notes for yourself and review them frequently - I'd spend the first hour or two of the week working example problems from the textbooks and creating notes on what we were learning. Then, I'd spend the other 4-5 hours a week doing homework and reviewing my notes and homework problems. Time after time the exams would include problems from the text book with a slight twist or different numbers. Since I had reviewed them often it was easy for me to get decent grades.
Once I had completed assignments and put in the study time for each course, I'd have the rest of day as free time. I also typically would take Sunday off from studying and just enjoy the day. I never had to cram for exams as I had already put in dozens of hours of study for each course. This allowed me to get good rest consistently and stay healthy with running.
Of course, I wasn't one of the really smart kids, so I had to study a lot more than some of my peers. You may be able to get by with less studying.
Good luck with running D1! I had an amazing experience and I hope you will as well.