Give me a few ways that I can get stronger and in better shape before the next ski season.

Skiing requires both muscular strength and endurance in your legs and core, and it is important that as you exercise these muscles your knees and other joints are strengthened as well. Some good leg and knee exercises to prepare for skiing include both normal lunges and reverse lunges, lateral jumps, and both normal planks and side planks. Improving your cardiovascular health is also important, although this can be done in any way that keeps your heart rate in Zone 2 or Zone 3 for an extended duration of time.