The number one thing most people leave out of their diets is protein. It is so easy to get yet so difficult. The general rule of thumb is for every pound of body weight, you want to get a gram of protein.
Now if you are trying to bulk up, it can be a little different. I personally try to get about 2 grams of protein per pound of body weight. It comes out to be more about 1.5g per pound of body weight but it's close enough.
The majority of my protein source is whole foods like chicken, beef, and turkey but I do take 3 protein shakes a day as well. I take one in the morning with breakfast, one right after the gym, or Post Workout (PWO shake is what you will hear by gym rats) and always one before bed.
The protein shake before bed is typically a slower digesting casein protein while the ones during the day are whey protein.
I will go into the types of protein later, this is just an introduction of my protein consumption in my daily fitness diet.