The biggest thing that is missing in most people's training is intensity. It's the single most relevant factor in determining the results you get from training. And here's the crux of most people's lack of results - they think they are training intensely when in reality they are not. So in their mind, if they think they are training with maximum intensity they have no reason to ramp it up.
Any time you go into a gym you'll notice more people screwing off than those that are pounding out an intense workout. You know the ones I'm talking about, they get in the way, they talk too much, and they barely break a sweat. If this sounds like your training MO do us all a favor and stay out of the gym.
It's time to take a good hard look at your training intensity level. And as a rule of thumb - no, as a guiding training philosophy, always make your next workout more intense than the one before. This progressive intensity is what will lead to results.