A healthy diet is MORE important for muscle gain than your training regime.

To gain muscle you need to be eating in a calorie surplus of between 250-500 calories EVERYDAY.

You MUST be eating clean foods ALMOST all the time. PRE-WORKOUT and POST-WORKOUT meals are vitally important to fuel your muscles for growth.

Related Questions:

1. What should I eat pre-workout and when should I eat it? 
2. What should I eat post-workout and how soon should I eat post-workout?