Principle

Single Responsibility

Each class should only do one thing. Avoid doing more than one (1) responsibility. If a class is for a the movement of a character, avoid including the handling of inputs.

Example

Instead of

public class MainCharacter() {
  public void Walk(Vector2 direction, float speed) {
    // Do walking
  }

  private void Update() {
    // Detect controller inputs
    // Call Walk(...);
  }
}

Do this

/* MainCharacter.cs */
public class MainCharacter() {
  public void Walk(Vector2 direction, float speed) {
    // Do walking
  }
}

/* MainCharacterInputHandler.cs */
public class MainCharacterInputHandler() {
  [SerializeField]
  private MainCharacter mainCharacter;

  public void Update() {
    // Detect controller inputs
    // Call mainCharacter.Walk(...)
  }
}