So essentially, more sets and keep the rest in between down?

I have started to do more sets, but your form starts to break down after 3-4 sets, so I drop the weight down as I go, hitting failure at each. By the end I'm at about 40-50% of my 1-rep max and fooked. Definitely makes the difference.
Doesn't just have to be your chest, can be done with any weights workout.