Pullovers should be part of any chest routine. Use them as one of the last exercises of the workout after other muscles are already fatigued.
Finish your next chest workout with dumbbell pullovers: 3-4 sets of 12-15 reps. Focus on squeezing the pecs to initiate the movement up from the bottom position and work on holding the squeeze throughout the rep.
Didn't it seem that the bodybuilders of yesteryear had bigger chests? (We're talking chest circumference here and not pec size, mind you.) Ellington thinks so and he knows why - it was all due to the all-but-lost art of ribcage expansion.