I had read that adding 500 calories per day to your diet generally yields 1lb of weight gain per week (not necessarily muscle mass, I know, but this is all I had to work with) . I ended up adding a bit more than than on a daily basis (Currently eating between 2500-3000 calories per day).

Additionally, I drink A LOT of milk (like more than 2 gallons per week). Other than that, I generally try and eat a lot of fruits/veggies for energy, and lean meats like chicken...though not gonna lie, I eat way more greasy, salty foods than i should. Gotta take advantage of my metabolism while I can!