6 ideas
We become just by doing just acts and brave by doing brave acts, the way builders become builders by building. A virtue is a settled state (hexis) laid down by repeated action, so character is the accumulated residue of choices already made. Knowing what is right adds little until repetition has trained the desires to follow.
Because the mean is hard to hit directly, steer toward the extreme opposite your natural leaning, as one straightens a warped stick by bending it the other way. First find which error you personally drift toward by noticing what gives you pleasure, then deliberately overcorrect. The target is relative to the person, not a fixed midpoint.
Each virtue sits between a vice of excess and a vice of deficiency: courage between rashness and cowardice, generosity between wastefulness and stinginess. The mean is not arithmetic moderation but the right amount at the right time, toward the right people, for the right reason. Some actions, such as murder or adultery, have no mean because the act itself is already the error.
Phronesis is the capacity to see what a particular situation calls for, and it grows from experience with particulars rather than from general principles. That is why the young can be brilliant at mathematics but not wise in conduct. No rulebook can replace it, because rules cannot anticipate the specifics that decide the right action.
Your character shows in what you enjoy doing, not just in what you do. The person who holds back from indulgence but resents it is merely self-controlled, while the temperate person finds the restraint itself pleasant. Watching where you feel pleasure or pain tells you how far a virtue has actually settled in.
An inquiry should seek only as much precision as its subject allows. Human action concerns variable particulars, so ethical claims hold 'for the most part' and must be sketched in outline, not proven like geometry. Demanding exact rules from ethics is as misguided as accepting mere plausibility from a mathematician.