Use compound lifts. It's important to focus most of your time end energy in the gym on things like deadlifts, squats, pull-ups, bench press, etc. These will give you your biggest muscle gains by a longshot. Isolation exercises are only an afterthought if you have extra time.
Work in the 2-10 rep range for the fastest muscle growth. Anything over 12 reps will not be effective for gaining weight fast. The 2 - 6 rep range will work on your strength and the 7 - 10 rep range will build size.
Never train for more than 45 - 60 minutes at a time. Cortisol is released at the 45 minute mark during your workout which is a catabolic hormone. This means your body is using muscle tissue for energy and you need to STOP working out and get food in your stomach quickly.
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