In order to be able to add any muscle weight to your body you will need some weight gain in order to work with. The kind of weight you will be putting on will be lean muscle weight and not fat. You need to understand that to put on this kind of lean muscle is actually a double process. You need to gain the weight but also eliminate the fat. For instance, if you gain muscle but also gain fat then you may be stronger but you are carrying around some useless weight as well. You will look larger but you won't have muscles that are leaner. So in order to do this you will need to eat the right food and lift weights.
It is important that you don't do something like this alone. If you can you should talk with a personal trainer about what is called regular resistance training programs. These involve multi joint movements and are very efficient for the growth of muscle because they actually stimulate multiple muscles all at once. It also accelerates your body's metabolism after, which means you are burning more calories when you are at rest.
You should consider sitting down and keeping track of everything you eat for several days. Once you have done this you should look at the calories that you have taken in. If you have not gained any weight with the food you have eaten during this time while doing your weight lifting then you may have to adjust your average daily calorie intake. This way you can figure out what your daily maintenance level will be in order to add that lean muscle to your body.
When you figure out what you are taking in, it's probably a good idea then to increase your intake to about 300 to about 500 calories more per day in order to make sure that you are getting enough calories to be able to add muscle. You need to make sure that the calories that you take in are from proteins that are lean like chicken breast and some tuna in water, never eat the tuna packed in oil.
You should also replace those simple carbohydrates like white bread or white rice with the more complex carbohydrates like whole wheat or whole grains like whole grain bread and brown rice. You should make sure that you include a lot of vegetables as well for they are also complex carbohydrates and so their consumption needs to be increased as well.
It is easier on your body if you eat small amounts of food at each sitting and this should be done every 3 hours or so instead of eating three huge meals a day. This is a good way to have fuel continually supplied to your muscles and doesn't really give the body that much time to store the foods as fat when you eat in this manner.
Make sure that you are performing a regular routine of high intensity training to keep fat burned off and to continue to boost your metabolism. This is why it's important to also include with your weight lifting some cardiovascular workout as well. This can be on a machine or it can be running, swimming, rowing, whatever gets the heart pumping is going to work.
Note: It is important to make sure that you divide your workout into different intervals where you alternate between a hard workout and a resting period then back to the workout. This should be done in 20 minute intervals. In other words work out for 20 minutes then rest for 20 minutes before moving onto something else.