Many factors go into whether or not you are actually building muscle or not. Things like rep count, workout frequency, routine type, nutrition, supplements amount of rest and so forth. Everyone is different but the right combination of the variables exists for everybody. But only ONE thing and one thing only keeps everybody building muscle once they find their way.
Since we are all unique, what works for some will not necessarily work for someone else. The way that I have managed to build mass over the years took many years for me to discover and may not work for you. I tried what I thought was all the text book ways of lifting for upwards of 5 years before I found the right mix for me. For the record, it turns out that low rep (4-6), very heavy weight, 90 seconds rest between sets, 5 pyramided sets, 2 body parts per workout, training 5 days a week was the way I finally started adding mass. Not to mention very little cardio work and heavy protein and creatine supplementation. I have many friends that have tried following my routine and it doesnt work for them, but they eventually found their way. But the same thing keeps everybody growing once they start.
Set a Personal Best ONCE in every workout.
Fine. How do I do that? Heres how and why it works.
Lets say todays chest day and you do 6 different exercises for your chest. If you are like most people you probably do the six lifts in the same order each workout and chart your progress. Hence the term chest routine. Once you start getting stronger you will grow but eventually plateau. Frustration sets in, you change your routine and maybe progress continues for a while. But when you go back to the original routine, you might actually be weaker, because you havent done these moves in a while. A common occurrence.
What works is this: Keep doing the same six moves in your original routine (they were working, right?), but change the order. You will obviously be strongest on either the first or second exercise because you are freshest at this point in your workout. So make that lift a different lift each session and during one of the sets of this exercise set a personal best for either most weight or more reps at your previous high weight. The trick is that you must perform at that level every workout thereafter. So now when you do this exercise next time, you are trying to match what was a personal best at a point in your workout when you are not at your freshest and strongest, as well as setting a new PB on a different exercise when you are, and so on and on and on.
If you do six exercises with 3 sets for each one, and follow this pattern, at the end of 18 chest workouts, every single set will be at weights higher than when you started 18 workouts ago. Which means if you hit your chest twice a week, in 2 months every set you do would be one that 9 weeks ago you couldnt. So, how big do you want to be?