Weight Gain Exercise Tactics:

Incorporate some strength training to your daily routine

Another excellent tactic is to target the larger muscle groups when weight training. Lift heavy, and target the legs, glutes, back and chest. Choose moves like the deadlift, squat and overhead press, because bigger exercises require more muscle recruitment and make for a more efficient workout. So drop the isolation exercises and train using compound moves. The more muscles (or joints) that are working during any given exercise the better!

You will also want to eat before bedtime to keep your body fueled at night so it doesn't wake you up needing nourishment. Sleep is also very important to build muscle and to keep your body performing well.