If you fail to enforce progressive overload, everything else you do is a waste of time.
Strangely enough, it takes a certain amount of muscle to lift a certain amount of weight. Funny how that works, right? Now, yes, I know beginners can get stronger largely by developing the neural aspects of strength production, but once you're past the novice stage, you won't get bigger until and unless you get stronger.
Most of us already understand the principle of progressive overload, but we're all prone to under-appreciating its importance in real world application, especially when those weights get heavy.
We often think we're progressing when we're not. Look back through your training journal and see if your weights for sets of 8-10 have improved on key lifts over the past few months. If they haven't, you haven't gained any appreciable muscle.
When your numbers get bigger, YOU get bigger, so know your benchmarks and make regular attempts to exceed them. As T Nation contributor Mark Rippetoe loves to say, "Hard and simple are the keys to big and strong."