Just like our extra resources in the relationships section of the book, this list is especially empty, because learning about attractiveness is a people-focused pursuit. I encourage you to direct all your attention to what attracts others most, doing your own research, and taking action on what you learn (do what the attractive people do). Here are a few quick ideas.
For inner attractiveness, building strong values, I recommend incorporating reflection into your daily life, which will allow you to come to lessons personalized to your life. For a great book on good values, check out The Way of The Peaceful Warrior by Dan Millman.
The most important part of physical attractiveness is building healthy habits while we are young. This article explains this well.
For hacking fat-loss, try this "diet".
For hacking muscle-growth, try this workout plan.