Hello!
Calculate your BMI and plan a suitable diet chart for yourself near a dietician. Quit alcohol and smoking completely.
Have a diet rich in proteins as in eggs, milk, soya, meat, lentils, beans etc with balanced carbohydrates, fat, minerals and vitamins along with physical exercise.
Take care!
Oh and on a side note..
Im 6''4' and currently after eating again weigh 170'ish Ibs im underweight very skinny im what some doctors would call 'Ectomorphic' basically thin and tall i have to work very hard to store both fat or muscle.