Train at least three times per week. You need at least three training sessions every week if you want to see significant muscle growth. If you are really new at weight training, this can be reduced to two at the start; however, you should increase the number of sessions per week as soon as you are able. If you already have some experience with strength training, you can add more sessions as well.
Remember that muscles grow during periods of rest, if you are trying to build muscle. So, try limiting your weight training to 2 or 3 days per week with a day of rest in between. On the off days, you could concentrate on doing cardio exercises to give the muscles a break.
If you have been weight training for a period of time and want to see results a bit more quickly, work on your large groups of muscles, such as those in your legs, back and chest. Some great exercises for those groups are deadlifts, squats, bench presses, dips and military presses.
Consider drinking a protein shake before starting your weight-training workouts. Liquid minerals tend to be absorbed quicker in the body than solid food, so think about having a shake filled with protein, about 10 to 20 grams. The protein shake will help give you a boost of protein to encourage protein synthesis, which is the way to building muscles.
Do not attempt extreme cardio training with weight training. Done within reason, this combo can be truly beneficial for your health, but when done in extreme fashions can contradict one another minimizing the results that you see from either one of them. Pick one to focus on and stay committed to working on it regularly.
Once you have completed this, you will understand that adding mass and getting in shape is not as difficult as it looks. While building the perfect body takes time, research and lots of exercise, the above advice will get you off to a good start.