According to Muscle & Fitness, you can achieve muscle gain by doing strength training exercises and increasing your calorie intake by approximately 300-500 calories above your BMI.
To increase the size of your body muscle, firstly you'll need to work out. According to Mayoclinic.org, strength training (also known as weight lifting) builds muscle, while cardiovascular exercise (running, walking, cycling) increases your cardiovascular health. While both types of exercise burn calories, cardiovascular exercise is generally done for the purpose of health, stamina and weight loss. Cardiovascular exercise is extremely beneficial to health and fitness, but is not necessary to gain muscle. Strength training increases muscle tone, size and overall strength. Greater muscle tone also increases the amount of calories your body burns in a resting state.
According to Muscleandfitness.com, to increase the size of your biceps specifically, you'll want to choose strength training exercises that isolate the bicep and other upper arm muscles, such as the triceps and deltoids. You can do this using barbells, weight-lifting machines at the gym or by doing calisthenics like push-ups. If you're a beginner, start off slower and work your way up to more difficult exercises. Generally, strength training exercises are done in three sets of 15 reps or more.
According to Muscleandfitness.com, another important factor for increasing muscle size is how much food you eat and what types of foods you eat. Firstly, you'll need to eat 300-500 calories above your BMI. Your BMI, or body mass index, is the number of calories you should eat daily that's based on your age, gender, weight and activity level. Your BMI is the calculated number of calories your body burns in a day from basic functions (like breathing and organ function), daily activities (walking, talking, taking out the trash) and exercise. Since your body needs calories to increase bulk, you'll need extra calories to build big biceps. But be careful not to overeat, or you will gain weight. You should also incorporate as much protein into your diet as possible (without overeating), because it stimulates muscle growth.