It can be tough to train for weeks and months without seeing the progress you are looking for. I've certainly been in that boat, and I know it is frustrating.
Especially, if you are putting in the hard work.
While it's true that building muscle is hard work, just working hard isn't enough. There is more pieces to the puzzle.
Sure, you could go in the gym and sweat your ass off and feel good about it, but that doesn't necessarily mean you will build any muscle.
So, let's breakdown the 8 rules to building muscle.
The effort needs to be there. Let's say you are taking on a set of 12 repetitions on a barbell squat. Reps 9-12 should feel like you are pushing up all of North America. You don't have to necessarily fail, however you need to come close. As Muhammad Ali once said "I only start counting, when it starts burning." Without proper effort, nothing else I will say in this article matters. You should not be breezing through your sets, or pacing yourself for the sets to come. Every set should be trained as if it were your last, and you should be resting between 2-3 minutes between your sets in order to ensure you are giving yourself enough rest to give a full effort for the next set.
You need to be doing a proper amount of volume. Volume refers to how many sets you are doing. You should be aiming for 10-20 sets per bigger muscle groups ( Chest,Back,Legs) per week. For example, if you want to grow your back, across the course of a week you might do 4 sets of a barbell bent over row and 3 sets of a seated cable row on Monday and Thursday to put you at 14 sets for the week. You also want 5-15 sets per smaller muscle groups ( Biceps, Lateral Delts, Triceps) per week. So that might look like 4 sets of lateral raises on Tuesday and Friday to put you at 8 sets for the week. Personally, I've met a good amount of people who tell me their muscles aren't growing, but they are not doing nearly enough volume.
Push heavy shit. Your muscles need a reason to grow. Your body naturally wants to remain as it is. Thanks to a concept known as homeostasis. Think of your muscles as that one stubborn family member you have. You have to try hard to persuade them, and you have to give them strong reasons to change their mind. The strong reasons you bring to the table relates to the heavy weight you need to be pushing. You should be pushing a weight that feels like there is no way in hell, you can get past 15 reps even on your best day.
Feed the muscle and allow it to recover. If you want to gain muscle mass, the weight on the scale should go up slightly. Preferably between 0.25lbs - 0.5lb per week. Once you surpass the beginner phase, It becomes very difficult to build muscle in a calorie deficit. Therefore, you should go into a slight calorie surplus. There is no reason to be too aggressive here, as you will just put on too much fat. So a good starting point is to take your maintenance calories (bodyweight (lbs) x 14-16) and add 200-400 calories to put you in a slight surplus. Adjust the numbers as needed, however this should be a fairly accurate starting point. Also you should be eating roughly 0.8g to 1g of protein per lb of bodyweight as well. Outside of this, you should be sleeping 7-9 hours a night and allowing your muscle 48-72 hours of rest before hitting it again. For example, if you trained glutes on Monday, don't train them again until at least Wednesday or Thursday.
You should feel the muscle you are working. Proper form is important. If you don't feel it, you probably aren't doing it right. Take the time to learn proper technique on exercises before doing them to reap the benefits of the exercise. If you are doing a lateral raise and you only feel it in your traps, your lateral delts are not going to grow. It's as simple as that. You shouldn't be so critical to a point where you are afraid to lift heavy because you feel your form will break down, but it should at least be good enough to feel what you are intending to work.
You need to progress your exercises. You will not build muscle unless you progress over time, that is your indicator. You should be pushing heavier weight over time, this can happen on a weekly basis, biweekly basis, or monthly basis. However, it needs to happen. For example, you could push 135 lbs on squat today for 10 reps, and next week or next month you should be able to push it for at least 11 reps. That is a great way to indicate you are building muscle. This concept is known as progressive overload.
You should lift both heavy and moderate weight. There are experts who swear that lifting heavy is the best way to build muscle, and there are experts who swear that lifting a moderate weight is the best way to build muscle. The truth is that they are both capable of building muscle, and it's best for you to do both. But, notice I didn't say anything about using light weights, because unless you are trying to learn the form for an exercise, they really have no use for you. So, you want to undulate between your heavy and moderate weight on a daily or weekly basis. For example, let's say you are doing 3 sets of the barbell bench press. You can split it up into a 10 rep set with a moderate weight, an 8 rep set with a moderate weight but slightly heavier, and a 6 rep set with a heavy weight. This would be a daily undulation. A weekly undulation would look like, 3 sets of 12 reps on the bench press this week with a moderate weight, 10 reps next week, 8 reps the week after that, and 6 reps with a heavy weight on the final week. Ideally, when you cycle back to the 12 rep mark, you want to pick a heavier weight than the first day's 12 rep set.
You must be consistent and you must be patient. I wish there was a way to speed up this process. Besides drugs of course. But, there isn't. Just like Rome wasn't built in a day, you can expect the same of your muscles. This takes time. But great things take time. And besides, what's the rush? Learn to enjoy the process, and aim to be ruthlessly consistent. The progress will come. In the meantime, enjoy it!
These are the rules of muscle building, not the suggestions. These are the principles, not the methods.
So yes, you will have to follow each of these if you want to build muscles. Outside of these, the methods are up to you.
If you want to do a dumbbell bench press rather than a barbell, do it. It's in your hands.
Play around with your methods, but stick by the principles.
And always remember if you need help, I'm always here for questions, and I've got a free 14 day challenge where I will help you build a program and assist you in the execution.
References
Clark, Micheal. NASM Essentials of Personal Fitness Training. Jones & Bartlett Learning, 2018.