The advice given for choosing the appropriate weight of dumbbells is to select weights heavy enough that the last couple of repetitions in each set are difficult to finish. If the sets are completed with ease, heavier dumbbells should be used.
This video is the second installment in Coach Ali's "Gains Home Dumbbell Workout Series." It's a home dumbbell workout focusing on back and biceps, suitable for all fitness levels. The workout consists of several exercises performed for three sets of 12 repetitions each. The instructors emphasize proper form and selecting appropriately heavy dumbbells.