How to we become virtuous, according to Aristotle?

One way would be to do what is expected of you, including your own school work. Fail. 

We reason that goodness is more than relative, that there are values that are universally excellent, such as kindness, justness, purity of motive, love of family and friends, and cleanliness.

These are understood by practical reason, and in enlightened self-interest we willingly put into practice such behaviors.

A modern version of this, confirming eudaimonia or being-cognition, is https://en.wikipedia.org/wiki/Maslow's_hierarchy_of_needs

 

I don't know anything about Aristotle, who was also a sinful man but the Bible suggests this: Because of inherent sinfulness, we must carry on a continuous inner battle to do what the course of virtue would require of us. If we are to remain virtuous, we can never allow ourselves to become slaves of sin. Instead, we must be “slaves to righteousness,” always thinking, speaking, and acting in a virtuous way. (Romans 6:16-23)