1. Train right
2. Eat right
3. Recover right

Train with heavy weights 3 times a week (M-W-F). Do one workout for the torso, the other for the legs and arms. Work up to 3 sets of 10 reps for the torso and arm work, 3 sets of 12 for the legs.

Eat A LOT. Eat 5-8 meals a day, with a protein shake before, during, and after your weight workouts. Use a high-quality whey-based protein powder. Add a multivitamin-mineral, fish oil, calcium complex, and a joint complex (glucosamine, condroitin, MSM). You'll need this to keep your joints healthy.

Recovery is the most-overlooked element of the 3 pillars of building muscle. Inadequate recovery is the reason most trainers fail when trying to build muscle. Get at least 7 hours of sleep a night (more is better right now, to a point, of course, 9 being optimal).

Because you're an athlete, and very active, you will need to eat more than you could ever imagine. Eat nutrient-dense foods and don't worry too much about fat content, as long as it comes from natural, unprocessed sources like beef, fish, chicken, milk, and eggs.

A great program that has worked for decades is the "Gallon of Milk a Day" program, where you endeavor to consume a gallon of whole milk a day (in addition to your regular meals). Couple this eating strategy with high-rep breathing squats and you'll be on your way to solid muscle increases.