I can only tell you from my personal experience...so here goes.
I'm definitely a type-A personality and very assertive in bed, but it was only recently that I was fully able to discover my dominant side. I was never demeaning or anything of that sort in the past because I didn't have a woman who was into that sort of stuff so I didn't explore it. A big stumbling block for me was thinking that I would scare or alienate the person.
Later I found myself in a relationship with someone that I truly loved and cared about, and she knew me inside and out. She knew I was a good person, loving and kind so I didn't worry about her being scared by me. This is where the fun began.
First of all
always remember that the sub is in control. You are not imposing your will upon them without their consent. They have the option to stop the action at any time. For me, I felt a deep connection in part because they were permitting me to let this side out and they enjoyed it. It was really hot and mutually had some mind-blowing sex.
Communication is key. Don't start off by gagging your sub. Give them instructions in a firm voice, and make them respond. IE: "I want you go to the bed and lie down on your stomach"..."Yes master". I didn't tend to get into dirty talk at this point yet. Simple instructions, given forcefully. If you know your partner well, you know what they like and that can be the reward (the hot) after the punishment (cold). Switch it up...back and forth.
I'm a fan of what we called "brutal loving", a kind of hot/cold session that accentuated the differences between the acts. For instance, spanking her ass HARD, and then lightly rubbing it and kissing the handprint. You can feel the welt and the warmth with your lips...it's fucking hot.
Here's a scenario I enjoyed. I told my partner to get on the bed, face down, ass up at the edge of the bed and cuffed her ankles and wrists. I would come up and say "You know you've been bad and I'm going to have to punish you"..."yes master, I've been a bad girl". Just an example. I enjoyed keeping a dialogue going that also had a side purpose of gauging how much she was enjoying it. With her ass up in the air in the prone position I would slowly circle around, stroking her skin. I'd walk up to the side and look her in the eyes and tell her she was bad, and then walk to the back again. Degrade her...call her a dirty little slut, or something like that. She's been BAD and she knows it. I'd slowly rub my fingers across her skin, and then *SPANK* her ass really hard. Then *SPANK*, *SPANK*, *SPANK*. You could see the welts start to form and I would lightly rub the welts and kiss them gently, enjoying the feeling of the hot skin...savoring it. Now that's the punishment...I'd say "You took that punishment so well...you are such a good little slave...are you ready for your reward? Then I would eat her out from the back and just love feeling her squirm and moan with delight. It's all about the contrast. There are so many more ways to do this...this is but one scenario.
Always have a safety word. If you are choking them, or have them gagged, have a signal such as tapping the bed or your arm. I have a background in jiujitsu so I am very good at choking people and being able to tell when im taking it to the point of passing out.
Feeling vulnerable and helpless is also something subs enjoy. I have eye bolts attached to the corners of my bed that I can attach ropes and chains to that clip into cuffs. Have your sub lie on their back, and shackle their limbs to corners. As they are splayed out helplessly, vocal messages like "mmmmm...you aren't going anywhere...I can do whateverrr I want to you." help convey the message and enhance the experience. This is a good scenario for a blindfold. I don't tend to prefer spankings, etc in this position, but more teasing, etc. nibbling...licking...stroking. Get up next to their face and make them suck your dick and tell you how good it feels in their throat. Make them squirm and want it really bad. If you are really toward the extreme end or an experienced BDSM player, a large (dull) knife that has been sitting in the freezer can be a very powerful sensation against warm, naked skin. I never got to try this but it sounds kinky as hell. Again...trust is key. A good way to segue into sex during this scenario is to unclip the ankle cuffs from the anchors so they are free, then come up between their legs missionary style and whisper in their ear "how bad do you want my cock right now?". At this point, your sub is probably really worked up and wants it bad. Make them beg for it until they are so wet they are practically dripping. I'd take their blindfold off at this point, look them straight in the eyes and say "I'm going to fuck you so good and there's nothing you can do about it". As I slip it inside of her I like to be staring her right in the eyes and be right on top of her so there is that combination of a deep connection and helplessness with her feeling my weight on top of her.
Man, I'm getting worked up just writing this out.
There's so much out there. My sex life was comparatively vanilla before this pandora's box was opened and there's no turning back. I love it, but only with the right sub. Always keep is safe, sane and consensual. You have to actively involve your sub, respect them, as they hold the control, and just have fun!
In the right situation it can bring you so close together that it's magical. I always liked to go progressively from her being a bad sub, to taking the punishment well, to being a good girl, and rewarding her, and as crazy as it sounds, this extreme situation can take you from brutality to some really profound, hot lovemaking, hence the term "brutal loving"
mmmmmmmmmmmmmm
Or you are the boss and she is your employee. You expect more than just word processing from your employees. Etc.
NOT! I didn't see one guy in there I would fuck. 
this thread. 
