You need to train and practice.

First, condition your brain. Watch nothing but hard rough sex, lots of Dominate/submissive scenes. Study them. Take notes. Act out the moves the men are doing. Jerk off to it. Make yourself like it. After a while of jerking off to this type of sex, this type of sex will be what you want and what you are aroused to. Kink.com is a good spot to start.

Get some props. Simple bondage tape, maybe a ball gag...just a simple belt to spank her with. This will help you. A blindfold is very good too for newbies. You need to build your self confidence with being a Dom, so when you blindfold her, it eases the pressure on you. You can then take your time and explore what you want to do to her.

Hell, even buy a simple $10 blow up doll to practice on. Practice grabbing its throat, slapping its face, pulling hair. Talking shit to it, spitting on it. Spanking it, whatever.... just so you have a object to kinda go thru the motions with.

If you really like her than you will do what she wants to make her happy. At least thats the type of person i am. I didnt like hard rough sex but the more women i got with, the more i noticed how much women really do enjoy this type of play. I got off on providing them pleasure but ive played with so many now that i really fucking enjoy it too now.

I have a lot of women that i hook up with that come to me seeking rough play because their boyfriends/husbands/whateevrs do not provide it to them.

So maybe if you arent the one giving her what she desires, she may very well find someone who does.

So throw yourself in it. Study the rough porn, jerk off to it, make yourself like it, act out little scripts, get some bdsm gear, and when you get with this girl, you become that fucking Dominating man thats deep down inside you. You take this slut by the throat and treat her like a whore. Shes going to open your mind and change you, this is a very exciting time for you!!! Wish you the best man!