To maximize enrollments, Teaching Institutions should make sure they offer courses for which there is a high demand: general education courses. The reason these courses are in high demand is because many Home Institutions use course sharing to give students options to take courses they may have missed in the general education sequence and/or the opportunity to replace poor grades they may have earned in these courses. To be sure, upper-level or niche courses have their market as well, as institutions may cancel these classes due to low enrollment or they may offer these courses very infrequently.
One way to ensure that you are offering courses in the highest demand is to create a list of the courses that your students take elsewhere in the summer and transfer back. This list will help identify courses typically used by students over the summer while also indicating an opportunity for your institution to bring enrollments back to your institution.