(note from Domina: The spellings here, "hir" "sie" etc. are unisex conventions. These indicate that it applies to either gender. These are deliberate, they are not misspellings.)
There are as many ways to do D/S as there are people, so you really need to know what your partner wants, doesn't want, is comfortable with, is afraid of, and so forth. A lot of submissives will have great trouble telling you what they want. For some of them, this is because they don't really KNOW what they want. Or, perhaps, they know how they want to feel, but they aren't sure what it is that will make them feel that way. Other submissives do have at least some idea of what they want, but they're too embarrassed to be able to tell you directly. And some submissives know what they want but feel as if it spoils things if they have to ask for it -- they want the impetus for the scene to come from you, and if they ask for something, then it's as if _they're_ controlling the scene, when what they want is for _you_ to control it. And of course, more than one of these can occur at once. A person can know only what it is sie wants to feel AND be too embarrassed to talk about it AND feel as if it gives hir too much control over things if sie tells you.
There are a couple of ways around these problems, but they all take a bit of work on the dom's part. For the sub who isn't all that sure what sie wants, you get hir to describe how sie wishes to feel. You ask hir what things in hir past have gotten hir to feel this way, even if it's only a small and mild version of what sie really wants. And of course you also use your knowledge of your partner to guess at what you suspect would make hir feel what sie wants. You get hir to tell you what sie fantasizes about (bearing in mind that fantasies are often more intense than anything a person would like to do in real life).
And you experiment. A scene doesn't have to last for hours. In the early stages, when you're just figuring out what works for both of you, you can try something for five minutes. (But just because the scene is short doesn't mean that you take it less seriously. You have to make these mini-scenes as real as your usual ones, or they won't work as a testing ground. Put your all into them, just keep 'em short.) Say you suspect that your submissive would enjoy wearing a collar. You put one on hir, do a few things with it, then take it off and ask hir how sie felt about it. If you and sie both liked it, you can always do it again for longer. But these mini-scenes let you try out things in the knowledge for BOTH of you that if you hate it, it only lasts for a short time -- this takes some of the pressure off. (When an ex-lover and I seemed to be moving in the direction of no-safeword scenes, I bought an egg timer. The idea was that he would have no safeword for the length of time it tooks the sands to run down. Three minutes is not very long, objectively speaking. But it can be a _very_ long time to someone who's never played without a safeword before and who realizes that this time there's no way out. I wasn't going to do a full-length no-safeword scene until after I'd seen how he handled the egg-timer version.)
For the sub who has at least some knowledge of what sie wants but who is too embarrassed to tell you what it is, there are a couple of routes to go. You can ask hir to write it down and give it to you, since a lot of people can write things that they cannot say. You can also try dominating it out of hir -- try winding your hand in hir hair, pulling hir head into a position that lets you stare into hir eyes, and demanding that sie tell you what you want to know right now. Or you can threaten some sort of physical punishment unless sie divulges the information (only with hir permission, of course. The punishment isn't really intended to be a motivator -- it's intended to be a way for the sub to save face with hirself. Sie can tell hirself that it's not greedy or forward or too bold or whatever to tell you what you want to know because you're _making_ hir tell you). Sometimes just letting hir tell you in the dark, when you're snuggled up with your arms around hir will be enough.
The sub who doesn't want to tell you anything because sie thinks that means that sie's controlling the scene or that sie's forcing you into something you don't really want tends to be a somewhat harder case, but there are a few things you can try. You can tell hir that you aren't promising to do any of the things that sie asks for -- you're just asking because as the dom, you have the right to ask any damned thing you please and to get an answer. "Since you are my property, the contents of your mind are also my property, and you will give them to me when I ask" is something I tell my submissive. You can tell hir that you want the information for your own selfish pleasure -- "Making you be submissive in a way that's good for you is likely to be ore fun for me than making you be submissive in a way that's bad for you, because the second way makes me work harder for less return. So give me what I need to know to get what I want."
Oh, yes, and a type I forgot to mention. Some submissives think that no one _really_ wants to dominate them, that you're just humoring them, and leaving you to your own devices is sort of a test. It's as if they're saying, "If you really want this, you'll figure it out on your own." My own submissive had a touch of this, so I just jumped in and started ordering him around, and once he was assured that I wanted it, too, his fantasies started pouring out.
Once you start getting information out of the person, there are a bunch of things you need to know:
1. You know sie's interested in D/S, but what kind?
2. What sorts of things does sie like besides D/S?
Okay. So now you know what your submissive wants. You also have to figure out what YOU want. It's easy, when you're first starting out and trying to figure out how to be a dom, to imagine some stereotypical stern, sneering dominant and try to emulate that image. But not all of us are cut out to fit that mold, and luckily for us, not all submissives _like_ dominants who fit that mold. You need to find _your_ personal style. The best style for you is not the one that's the closest to the stereotype, it's the one that makes your eyes light up and your energy rise and makes you feel that THIS is the alivest you've felt in a long time. Personally, I'm a pretty gentle dominant as far as manner goes, but manner can be deceiving. One of the things I like to do is to force my submissive to do things that he wants to do but is too frightened to do -- the "You are so much mine that I can make you do something that terrifies you" feeling is quite a rush for me, but I know I can let myself give in to that feeling because I'm making him do something that he secretly wants. I also like mental stripping -- making my slave be mentally and emotionally naked with me -- he must tell me anything I want to know about him. Oh, and making him scream is fun, too. :-)
Of course, your style will be influenced by your submissive's style. The sort of submissive who wants to be forced into submission will elicit a different response from you than the sort of submissive who wants to lay hir submission at your feet like a present. And of course, some submissives can do one thing at one time and the other thing at another time. Just to keep you on your toes. :-)
Don't worry if it feels sort of strange in the beginning. When I first started dominating my slave, I would look at my face in the mirror and chuckle and say, "This is NOT the face of the sort of person who owns a man." But that "WHO? Sweet little me?" feeling wore off after a while. That "I'm not cut out for this. I don't know what I'm doing" feeling wore off after a while. If it's TRULY not for you, don't force yourself. But do give yourself a little while to try it on and get used to it before you decide whether or not it's for you. I felt silly and nervous and out of place at first. But after a while, I came to feel that there were few things I'd ever done that were more satisfying.