Building muscle has just as much to do with diet as it does with training, if not more.
You can't build muscle without a calorie surplus, just as you can't build muscle without resistance training.
To build muscle fast, you have to optimize your diet as well as training regimen. Here is how to do it.
1. Avoid Low Carb Diets
While low carb diets are great for cutting fat, they won't help you with gaining muscle mass. You need carbs for fuel so you can exercise more efficiently.
Carbohydrates are important before training sessions, and immediately after training sessions. Carbs are your muscles primary fuel.
By consuming complex carbs you restore glycogen stores within your muscles[1] for further activity and fullness. This is a major factor in how effective a training session is.
2. Avoid All Alcohol
Alcohol, even in small amounts, can have major effects on sleep, and recovery. In a study conducted in 1980, alcohol in small doses (0.8 g/kg) before bedtime, suppressed plasma growth hormone by 70%-75%[2].
If you add in the effects of dehydration and release of cortisol, it's nothing but a recipe for disaster.
3. Get More Protein
There is a lot of confusion surrounding protein these days. One article says your not eating enough, the other says your eating way too much.
So what is the key?
For moderately active, and highly active adults, it is reasonable to consume around 2-3 grams of protein for every kilogram of bodyweight.[3]
Studies show that too much protein intake has an extremely low chance of negative side effects. Plus, protein is essential in so many bodily functions.
4. Lift Heavy Weights
Protein alone cannot build muscle. To really add-on size, you must lift heavy weights. Or use your bodyweight to achieve the desired resistance.
In the gym, you could focus on lifting 6 sets of 6 reps with a heavy enough weight to reach failure in the last couple of sets. This should be enough to make some serious gains.
5. Switch-up Your Workouts
This doesn't necessarily mean changing the exercises. Vary your sets and reps, rest time, and intensity. This will help you break through those dreaded plateaus.
I hope this list helps you in achieving your desired physique. But this can only help you if you continually take daily action. Avoid analysis paralysis, and just get to work.