There are two main things to consider when it comes to newbies packing on muscle mass 1.) Diet, and 2.) type of resistance training. Diet is a given, you need an optimal balance between calories, protein and carbs to ensure you feed muscle to prompt growth. However, all too often people will go into the gym and focus on nothing but chest and biceps, then the next day they’ll target the triceps and back, and then maybe do a little legs in order to grow. This will work to an extent, but if overall muscle mass is your goal then you will see far quicker gains performing compound movements such as deadlift, squats and bench. The nature of these movements mean you recruit a number of muscle groups as well as spiking hormones such as growth hormone and testosterone.
Don’t waste time focussing on individual muscle groups for the first few months, earn the right to develop those peaked biceps, or those sweeping quads by hitting the compound moves.