When it comes to building more muscle mass and strength, how many times you workout a certain muscle group is just as important how often you work that muscle group. In basic terms, getting in the correct volume of sets and repetitions per muscle group. One way to kill two birds with one stone is to perform total body workouts. When you do total body workouts, you workout large muscle groups all at the same time if not the entire body.
Outside of the gym, most of the things you physically pick up on a daily basis are not in the form of dumbbells and iron plates. More or less, common things such as picking up your child, carrying grocery bags into the house and mowing the lawns are examples of such. In simpler terms, one way to increase your strength and muscle mass is to train with odd ball objects such as kettlebells, medicine balls, thicker girth barbells to change up your strength training routine.
Another basic exercise to increase strength and overall muscle mass is to regularly perform pull ups. Pull-ups are one of the best upper body exercises to do because of muscle involvement and for the very reason you are training with your own body weight. Pull-up strength can be applicable to relatively how strong you are for normal standards. If you can already do 10-15 pull-ups with perfect form, you are already on the right track. 5-10 is average for the normal human being, but anything less than that might be time to incorporate pull-ups into your daily if not weekly routine.
You do not have to kill yourself for an hour hour doing pull-ups, that would be over training. If you are a beginner, do one set of pull-ups once in the morning and once before you go to bed. Do each set for the max number that you can do, even if it's for a few repetitions. If you can barely even do one repetition, you can either use the assisted pull-up gym located at any big box gym or you can perform negatives. To perform negatives, use a stable platform such as a chair or stool below the pull-up bar to start yourself at the top of the pull-up bar. Slowly lower yourself as slow as you can to perform one set. Doing a few sets of these once a day for repetitions of 5-10 is ideal.