The discipline if assent is essentially stoic mindfulness. We must be careful not to accept every impulses that we receive as fact. To do this we must keep watch over our minds so that our desires and actions may not be corrupted.
Readings: The Discourses of Epictetus Book 3 http://classics.mit.edu/Epictetus/discourses.3.three.html
The Enchridion #1 http://classics.mit.edu/Epictetus/epicench.html
Also check out the Encyclopedia of Philosophy it was a great reference! http://www.iep.utm.edu/epictetu/#SSH4eiii