Gaining muscle mass can be a problem for some people. Doing the wrong workouts makes this difficult. You won't be able to increase your strength by using body-part split routines. If your exercise routine is working, then you should be lifting more than you were a month ago. The more strength you have, the more muscle mass you will have. To fix your mistakes and make your muscles bigger, here are some tips to follow.
How to build more muscle mass? Increasing your muscle mass means getting stronger. You can do a strength based exercise to achieve this. Increasing the weight you are lifting does this. You don't have to change exercises every week, stick to a couple different lifts and stick with those. Every week or two, increase the amount of weight you are using. You also don't have to lift until you can't anymore. Training until failure will overwork your muscles. Increasing your repetitions won't do as much good as increasing your weight.
If you have a muscle that you want to get larger, you don't have to work it directly. Exercises work out more than one muscle at a time. You can make a muscle bigger if you work the muscles around it as well. For bigger biceps you should do barbell row, and for bigger legs you should do squats. These exercise the whole part of the body which will work much better. Training one muscle will also lead you to look disproportional. Read http://en.wikipedia.org/wiki/General_fitness_training to know more about general fitness training.
Another common mistake is using machines instead of free weights. Free weights are harder for your body because they build real strength that translates outside of the gym. You are in charge of balancing the weights yourself when you don't use a machine. Using your muscles this way will help build strength. Balancing the weights yourself will strengthen your stabilizing muscles as well as the ones you are focusing one. Doing the awkward motions of the machine can also cause injuries. You do more natural movements when you use free weights. You should also use barbells instead of dumbbells. Dumbbells are harder to position and don't allow for progressive loading.
You should also try and train several times a week to increase your muscle mass. Two or three times a week is a good amount to start at. Don't go too much over that or you may overtrain. You will just be sore and weak if you train more than that at www.howbuildmusclemass.com. You have to build up to that kind of training because you need time to let your muscles recover. You have to eat enough to supply the nutrients when you are gaining muscle mass. Eating unprocessed food, plenty of protein, and at least a gallon of water every day will contribute largely to your success. You also have to be consistent.