Even a small, easily tradable dog like the Cavalier King Charles Spaniel must of course enjoy a good upbringing so that he knows what he is allowed to do and what is not and so that he is reliable in every situation. Getting to the basics with him is usually more fun than work.
If you want to practice commands with your protégé, it is a great advantage that the cute four-legged friends are so docile. They are also smart and enjoy dealing with people. If you teach your dog "sit" and other important commands in a playful way and praise him extensively for his good behavior, or consistently but gently forbid undesired behavior, you should reach your goal quickly.
If you want to practice with him to listen to your call, you will surely benefit from the fact that the attached dog is so happy to be with his person that he will not be asked too long. Play a little with him as a reward, and the little spaniel will remember well that he will listen to her so well next time.
In socialization, for example, proper behavior in relation to other animals and children play a role - but the tolerable and very child-loving spaniel will also be naturally very uncomplicated, because starting quarrels is not his thing at all and he is almost known for it to be friendly to everyone.
Nevertheless: Better safe than sorry. Visit a dog school with your four-legged friend and get him used to all kinds of normal and unusual situations right from the start. Also make sure that your dog is always well used. And be careful: the little dog is so charming that it is sometimes difficult to be with him as consistently as a good dog training requires.