There are two basic ways for a sub to submit to her Dom: the easy way, and the hard way.
The easy way is for the sub to simply give in, agree to do (or not to do) whatever the Dom has ordered. Immediate and complete submission.
The hard way is for the sub to refuse, steadfastly, to follow orders. To stomp her foot, cross her arms, look at him mulishly, and say NO. The ultimate act of defiance.
There are varying reactions between these two extremes, of course. A sub might balk at first when handed instructions, but ultimately comply. Or she may pretend to be willing to go along with instructions at first, but then later try to sabotage the lesson in a passive but perversive sort of way. I happen to think the former scenario is easier to mend than the latter. A sub who, once forced into submission, can be trusted to carry out orders, is much better than a sub who must be watched at all times for any sign of subterfuge.
Negotiations are often involved, though. Especially when they are new orders, instructions to do something the sub has never done before. If they include an act that will push the sub's buttons, push her boundaries, a Dom must treat carefully and make sure he is not stretching the sub's limits too far at once. If it something he knows will be very difficult for her, lots of support and encouragement may be needed, and a reward after the orders are carried out would probably also be nice.
Now if the sub is being ordered to do something she's already done before, maybe even many times, and it's well within her ability and aptitude, but she balks anyway, that's usually a sign she needs to be taken in hand, shown a good demonstration of power by her Dom. She may balk because it's been a while since he's had to reprimand her, and she's 'forgotten' her place. Or it may be she really gets off on a good spanking, craves what has been denied her for too long, and thinks the only way to get it is by misbehaving.
Sometimes, being refused a good spanking is a form of punishment. Especially if it's given with disdain: "I am so disappointed in you right now, it's not even worth my time to try to correct your behavior. Maybe in a little while, when I think you are in a mindset to actually learn something, I'll try to teach you some good manners." It's like a time-out, only with a heavy dose of humiliation and contempt. It's another way to show the sub her actions have gone too far.
The more the sub and Dom get to know each other, the better the Dom will know the sub's levels of comfort, her soft boundaries, her hard boundaries, and--what can often be the most fun to handle--the things she wants to be forced to do. I think every woman has one or two things she wants to do, but for one reason or another, needs to be strong-armed into it. Maybe it's trying a new position, or playing out a fantasy role...or maybe it's experimenting with what she considers to be a very naughty toy. Whatever it is, once the Dom discovers it is one of her barriers that really, she wants broken, it is only right for him to do whatever it takes to fulfill her need.
In the end, they will be both be happier for it.