We always love ourselves, even when we do not like what we do. Loving ourselves simply means that we want good for ourselves, we want to see ourselves succeed and do well. Even when we are frustrated at our mistakes or saddened by our shortcomings and failures, we still want to see things turn around for ourselves. This is the same kind of love we ought to have for others. Some people are easier to like than others, and we often have a natural fondness or affection toward certain types of individuals. Lewis says there is nothing wrong with this, just like there is nothing wrong with having certain foods that we like and dislike. The problem comes from what we do with those natural likes and dislikes, how we treat people because of them.
Liking someone, of course, makes it easier to be charitable toward them, and it is fine to encourage affection toward people, but "it would be quite wrong to think that the way to become charitable is to sit trying to manufacture affectionate feelings."
The same is true in the opposite direction too. The more you injure someone you do not like, the more you treat them unkindly or think or speak badly about them, the more you will come to dislike them until your hate for them and your cruelty toward them become a vicious cycle that feeds itself. This is why Lewis says we must be careful about every little decision we make. The smallest kindness, the smallest loving act we do today "is the capture of a strategic point from which, a few months later, you may be able to go on to victories you never dreamed of." And the seemingly trivial indulgence in hatefulness or anger or lust today can open up the gates and make one vulnerable to attacks later on that would have otherwise been impossible.
Lewis makes one final point about the virtue of Love when it is between us and God. Really, the same principle applies here that applies between us and our fellow man: