There is no one magic exercise for the back. It needs to be trained for both width and thickness. That means all the different types of rows and all variations of pullups and pulldowns.
Learn to connect your mind to the muscle. When doing rows, instead of simply pulling with your arms, feel it in your lats, rhomboids, teres major, teres minor, and all the other muscles of the back you are trying to build.
Go to the gym with a specific workout plan, but don’t be afraid to deviate based on how your body is feeling that day.
“To become a champion, to be the best, it can’t boil down to a formula of sets and reps. It’s the accumulation of all the knowledge and training that person has done over the years.” —Kai Greene
GREENE’S BACK WORKOUT
Wide-grip Pullup: 4 sets, 8–15 reps
Lat Pulldown: 4 sets, 8–15 reps
Barbell Row: 4 sets, 8–15 reps
T-bar Row: 4 sets, 8–15 reps
Seated Cable Row: 4 sets, 8–15 reps