First of all you need to change your routine as your body should be fully prepared to undergo a transformation. The right combination of your sleep, food, exercise can help you to hit the mark in less time. You should sleep at least 8 hours daily. Eat healthy and go through a proper exercise routine.
Exercise properly as it is very important to avoid the side effects of weight gain. You should consult fitness coach/trainer to choose right style of exercise. If you cannot afford to join a fitness club then you may start with simple weight lifting, push ups, chin ups, bench press, stretching etc.
Try free weight exercises that put most stress on muscles and stimulate the maximum number of muscle fibres. You can have the assistance of dietary supplement but it is better to stick with the natural method. You should go for balanced diet which comprises right amount of fats and proteins.
Mostly, people think that junk food helps to gain weight quickly it is completely a wrong notion. It deprives your body of nutritious elements. You may replace those tasty burgers and sandwiches with starchy food like potato chips. Use as much dairy products as you can. Add meat, butter, fruits, yogurt and eggs in your diet.
Stop eating between meals rather stick with three large meals or five small meals a day. Choose food that carries calories and healthy fats, Increase your intake of protein.
Once you have achieved your goal do not leave this routine as your body will only respond to a consistent schedule. Moreover, lack of exercise and activity may result into a plump and unhealthy body.