1. Eat more calories than you burn.
2. Increase your portion sizes.
3. Eat nutrient-dense foods like lean proteins, healthy fats, and complex carbohydrates.
4. Eat regularly throughout the day.
5. Drink plenty of fluids.
6. Get enough sleep.
7. Add healthy snacks to your diet.
8. Try weight gain shakes or smoothies.
9. Exercise regularly to build muscle.
10. Consider taking supplements.