forget doing dumbell exercises at the mo, concentrate on heavy barbell work and compound lifts (deadlift, squat, benchpress, military press, barbell curls) if you wanna gain size, try and have 2 days rest in between workouts.

Dont just work till your tired, use a heavy weight so u can only perform around 32 reps in total ( 4 sets of 8 reps) and try to stay in the 6-10 rep range.

PS: WORK THE LEGS!!! dont neglect them, by working your legs you will increase overall body mass, including your UPPER BODY!!!