Just like we did on Day 1, we're going to train a main mover and a synergist. The main mover today is your back, while your biceps will act as a synergist. Each time you pull, your biceps will engage to help out. However, it's your job to make sure your biceps aren't doing all the work.
For each exercise other than curls, you'll have to concentrate on using your back to do the moving. Think of your arms as nothing more than levers holding the weight. The action of the exercise should be driven almost entirely by your back.
If bodyweight chin-ups are too easy, add weight. These reps should be difficult enough for you to fail between 6-8 reps. Remember, we want that first exercise to be heavy. Don't go easy—you get two minutes to rest between sets.