Calories are king when it comes to building muscle, but the macronutrient breakdown is also important. Here are some simple guidelines:
Shoot for 1 gram of protein per pound of bodyweight. There appears to be no major benefit to consuming more protein if you're a drug-free lifter. Still, if you're having trouble getting your calories, feel free to get more protein. Just realize it may not be beneficial, at least for muscle gains.
If you're lean enough, carbs are your best friend for building muscle. Carbohydrates are protein-sparing, meaning they'll prevent the breakdown of muscle tissue. Similar to banking, a penny saved is a penny earned. Consider carbs the key to saving the muscle you already have while promoting further growth.
Men who are 7-12% body fat and women who are 17-19% body fat should aim for 2 to 2.5 grams of carbs per pound of bodyweight.
Men who are 12-15% body fat and women who are 19-21% should try 1.5 to 2 grams of carbs per pound of bodyweight. If you have a higher body fat percentage, get lean first. But overall, far too many lifters suffer from carb-phobia. As a result, they stay smaller and weaker than they need to.
The remainder of your calories should be from fat. Yes, there are exceptions. Some folks do better on a higher fat diet.