The good sub
For the moment the power is given, the responsible Domme is what makes a sensual, sensible and desirable submissive. To get to this point the most important quality in a good sub is his ability to make personal connection with the Mistress he aspires to serve.
Intelligence, common sense, and open mind are relevant for the good sub and the good Domme as well. The good sub is not stupid, mindless or even weak. In fact to surrender power you need to have to intelligence to make an informed decision. His willingness and his mental availability to serve and his capability to reveal his inner self makes his desirable for his Mistress. This way she will appreciate his sensitivity and genuine wish to seek for his Mistress pleasure.
This good sub needs to trust his Mistress enough to reveal his vulnerability to his Mistress. This requires a certain amount of courage and bravery .. and willingness to please. He accepts his desires to be sensually submissive and finds joy in being used for his Mistress pleasure. This way he will find the freedom of letting his Mistress explore and appreciate what he is and how to use him. This good sub will also support his Mistress to see that her needs are met.
All of this being in mind, this sub will make sure to follow rituals expected form his Mistress. To indicate clearly his status towards her. When it comes to specific techniques he will continue to improve his skills and ask for directions on how to do better for her.