If you consider the body topology I have designed for my character. You might wonder why the topology is lined up the way it is. If you remember all 3d models are created with a specific purpose in mind and If you look at my character and think about how it is expected to move. You will see that some edges line up with where the body will bend and others where the body gets fat or thins out. These are called key and fill edges
1. Key edges are those that will be bending or controlling a bend.
These usually have the bone axis point sitting under them.
2. Fill edges are those that fill out or help shape muscle or body bulk but don't deform majorly when the bone moves underneath.
Design your characters with the key edges in mind first.