The secret is....there is no secret. Everything you need to know is already out there at your fingertips for your use. But let's go over the key points to make sure you have all the needed resources to be able to push yourself in the proper direction.
The most important aspect of hypertrophy, the gaining of muscle tissue, is that you have to be in a caloric surplus or the gaining of muscle is already at a non starter. First, calculate your basal metabolic rate to know what the bare minimum amount of calories your body needs a day. From this add 10% of the overall value to put yourself in a slight surplus. MOST OF THESE CALORIES SHOULD COME FROM CARBS AND PROTEINS. Sticks of butter don't build physiques. Start here and increase your calories slowly so you see about a half pound increase, week to week, on the scale. If you consistently do this over the course of 12-16 weeks, you will see increases in muscle mass. But how much muscle? Let's discuss.
The way to preferentially build muscle over fat, outside of macronutrient breakdown, is to force adaptations in the weight room. There are two variables that effect our ability to force adaptations; Intensity and Load. Intensity is how close to failure you are. This can be counted in Reps in Reserve, Rated Perceived Exertion, or any other system that you find useful. There has to be a consistent effort to push the intensity in the gym in order to force adaptation. This is load aside! In order to gain muscle a 30-75% 1RM weight should be selected and taken to a high degree of difficulty in the 6-30 rep range. NO ONE REP MAXES. NO HEAVY TRIPLES. We aren't powerlifting at this point we have the ultimate goal of building muscle tissue so make all efforts geared towards that.
The final component in our muscle building triad is recovery. What are you doing to make sure that your body is ready enough to go train? Sleep is paramount. Are you getting 7-9 hours of sleep a night? If building muscle is important enough to you that you have made it this far into this article then you better be! Is your water intake AT LEAST at a gallon of liquids a day? If the answer to that was no then guess again. Are you training seven days a week because that is what it takes? Wrong stop doing that dumb shit. Give yourself time to rest. Dial back the volume of days and you will be surprised how much better you feel and you might also get some of that sweet, sweet progress you have been begging for.