How to gain muscle as fast as possible?

Im 15 years old, 5ft9, and 11 stone, i play football, rugby, Mma ( mixed martial art) and box, i have my own gym in my garage this consists of a multi-gym ( lat bar, rower, butterfly press, machine bench press, leg curl, and biceps curl, i also have a free standing weights bench, dumbbells, and barbells, a pull up bar, and medicine ball, and a ab machine) could some-one tell me how to gain muscle mass fast, or come up with a regular work out for me? many thanks