Many of these things intertwine with each other. But all are my personal beliefs of what makes a good submissive as well as a good person. Most of these can be applied to any relationship, not just those within BDSM. I list them in alphabetical order for ease of reading.

Acceptance:
This is the ability to see and accept yourself for who and what you are, be they your good points or your bad ones. This includes knowing your limitations yet keeping the thought that things can change and knowing you will change as well. This is the ability to let yourself be who you are, to take pride and pleasure in the person you are, and not lose that acceptance because someone said you are not what you know you are. 
 

Communication:
This is the ability to talk openly and honestly about what is in your heart and mind, your opinions and beliefs, your needs vs. your wants, your responses or reactions, basically to be able to talk about everything. This ability also calls into play the honesty of the submissive and the dominant. Once open communication has been established it should remain that way and will do so provided the submissive does not stop communicating honestly. To not communicate is to endanger yourself physically (as well as emotionally). Communication need not always be verbal. Just so long as what you need to say to your partner, gets said to them, then the lines of communication stay open. For example, you may find a particular topic easier to write about in your journal and thus "tell" your partner that way. This is still communicating.

Courtesy (aka Manners):
This one is fairly self explanatory but many people have asked me for specifics on courtesy. Since the specifics of this one vary with each relationship, I will only address general manners. It is the ability to show proper courtesy by using please and thank you, addressing people with general respect and courtesy.

Grace:
This is another whose specifics vary with each relationship, but is basically the ability to not appear stilted or halting in your movements. I'm not sure this one is of major importance to many people, but I list it here anyway as it has come up frequently. Of course this may be affected by physical limitations that will reduce its importance.

Growth:
The ability to grow within yourself, look for and attain new goals. Be these mental, emotional or physical goals. The ability to continue to grow and sharpen your abilities is very important as it prevents the relationship from stagnating, helps you to grow as a submissive and thus discover new ways to please or serve your dominant.

Honesty:
 Personally I feel this shouldn't need to be said, but there are far too many people who lack honesty so it has to be said. Honesty is the ability to speak up, be open and truthful about what you say. Don't hide your emotions, fears, limits, fantasies, ideas and thoughts. Don't tell the dominant what you think he/she wants to hear. A successful submissive is an honest person, one who does not lie, deceive, or intentionally manipulate. Honesty builds trust. Trust is the basis of a relationship. To lie, breaks down the trust and therefore the relationship by removing it's very foundation.

Humility:
 This is basically the ability to see yourself as fallible. A successful submissive knows they will make mistakes; that they are not perfect. A successful submissive admits his/her mistakes, and strives to correct them. Giving off an attitude of being better than anyone else, is not a desired trait. Having a sense of pride is good, but humility is necessary to prevent one from being arrogant.

Intelligence:
By intelligence I don't mean book smart, the ability to do long involved mathematical equations or pull apart and rebuild a computer. As it applies to a successful submissive intelligence is the ability to think for themselves. The ability to make informed decisions about who to submit to and just how far their submission goes. The ability to take the time to learn their partner outside the roles of dominant and submissive, to learn them as the person they are, their likes and dislikes. The ability to learn what pleases their dominant and remember those things. 

Loyalty:
 This is a very important trait in a submissive. It is the ability to uphold your dominants rules over anyone else. A successful submissive will not act in a manner that will raise doubts about his/her commitment to their dominant. It is upholding your end of the agreement made with your partner to the best of your abilities. This can also mean standing by your partner when difficulties arise. This tends to come hand in hand with commitment and both are necessary for a long term relationship to survive. 
 

Obedience:
This is exactly what is in every day life, the ability to do what you are told. Within a power exchange relationship this means willingly following the terms of your dominant and doing what you are told. Willing obedience is pleasing to the submissive as well as the dominant. This can directly relate to the person's submissiveness. A submissive does not obey because they fear their dominant, they obey because they have an intense need to please the dominant. This does not mean blind obedience (never question anything). Specifics regarding obedience do vary with each relationship, but obeying one's dominant is part of a power exchange relationship and is expected.

Open Mind:
This is the ability to view things with as little preset prejudice as possible. To maintain the ability to learn new things and be open to trying something new or different. It directly compliments Growth. 

Patience:
 That is the ability to wait for things. Being pushy is aggravating. This does not mean to push your most urgent needs aside, but to learn the difference between what is a necessity and what is not and to convey these things to the dominant.

Pride: (self respect, self esteem)
This does not mean be arrogant, just the knowledge of your ability. Having a sense of pride in your abilities shows that you have a healthy sense of self esteem and your whole identity does not rely on another's point of view. A good submissive values themselves and respects their own limits. A solid sense of self esteem is a necessity for a submissive or they can become co-dependent upon the dominant, relying on the dominant for their own mental picture of themselves. Humility is part of this as well. 

Respect:
The ability to show respect through one's tone of voice, manners and general attitude. A sub must respect their dom (unless it is destroyed) and be respectful to others. This goes along with manners. Showing respect to one's dominant should be at all times, and not just when the submissive feels like it. Yes, we have arguments in these relationships, but a submissive should strive to maintain a respectful demeanor even during such times. 
 

Service:
Willingly completing tasks (sexual or otherwise) set for you by your dominant. As well to apply your observations to the things you do to please your dominant. Service usually points to those things outside of sexual ones and play (sessions). Such things as housework, cooking, and other things designed to make the home of the dominant more pleasing to him/her. Service can include tasks set for you by the dominant which do not fall under household chores. Perhaps the household budgeting is one task the dominant sets upon you, cooking his/her favorite meal, and many other things can be service. Basically anything done with the direct intent to please the dominant in some manner can be seen as service.

Submissiveness:
This can be taught or an inherent personality trait. This is the need to please others and by doing so pleasing yourself. As well, it is the ability to give in (so to speak) to another's control and feel content doing so. Submissiveness as a learned behavior does occur in bdsm relationships. This usually happens as the submissive gains experience and thus grows in their submission. However, if a person has to learn to submit against their natural inclinations not to, then submission is probably not for them. 

Trust:
A submissive must be able to trust themselves, the choices they make and be able to trust others. An overly wary or closed submissive, will have a more difficult time attaining a good relationship with a dominant. Being able to trust your instincts is necessary for a submissive, specially when looking for a dominant because your instincts will often tell you if something is not right. Listen to them because to ignore them can be dangerous.