Like behavior begets like character.
If you want to be just, act justly. There is a rub. If I'm not just, I can't act justly. But I can't get the virtue by not acting that way. Catch 22.
If you are not just, you can't act justly. But what you can do, is act in accordance with justice. To act in accordance with justice is not to act justly, it is to do that which just if you were just. How do I mimic justice? By finding a just person and watching him live.
This principle (according to Aristotle) works for vices as well.
Illustration of a habitual liar.
Acting in accordance with virtue would be to do that which would be virtuous if you were virtuous.