Simple.. you need to eat more than you currently do. That doesn't mean you need to immediately double your calories, that will only make you fat. The real goal is to increase nutrients at the times of the day/night when they will be most beneficial to your recovery, but not at times when they will just go unused. Ideal times would be peri-workout, first thing in the morning, and not just increasing cals, but making sure they're worthwhile cals before bed.
Remember, you can't force feed muscle growth. The human body doesn't work like that. You can however provide a better environment for recovery and growth, as well as providing more raw materials to accomplish your goals.