If a person wants to turn away from evil, he need not take any action in order to remove the evil from himself, since there is a rule in nature that a person cannot stand something bad about himself.
Rather, when a person realizes that something is harmful and bad for him, that it could make him lose his life, he immediately turns away from it and stays far from its reach. It follows that turning away from something bad comes to him without any work.
Rather, the work is to come to realize that this thing is so harmful that he cannot go on with it in his life. To come to this, we need “good.” By engaging in Torah and Mitzvot [commandments] and wanting to achieve the complete spiritual life, one can come to the recognition of evil. When he achieves this recognition, he naturally turns away from evil. This is the meaning of “do good.”