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For getting rough and being dominant, it helps if you are dominant first of all. If you aren't very comfortable, the first thing to be able to get comfortable with is simply changing the position you are in. Do this by physically moving the girl to a different one. i.e. If you are doing missionary, come out and move her body so you can spoon her. This movement will already shows dominance and a girl will readily comply.
When you get more comfortable with handling a girl, take her against a wall from behind. Pushing a girl flat against the wall gives just a ton of dominance opportunities. You can grab her hair and push face gently against the wall while turning it so you can kiss her mouth. You can pull her arm toward you so you can get at her mid section. You can also use your whole body to flatten her into the wall. This seems to drive girls completely nuts.
Moving from any position to her being on her belly also gives you an opportunity to spank her. Just make sure you give her a real zinger by slapping hard, but as soon as you touch pull your hand back. You should practice on your own leg a few times before trying it though. You know you are doing it write because it makes a high pitch noise. If you just smack a girl and don't get the noise, it's not as nice.
If all of this is too difficult try simply holding firmly on her arm below the bicep, taking her jaw in your hand and drawing it towards you to kiss her, or firmly, but lightly grab her hair in the middle of the back of her head.
My personal favorite is biting, but I've left some pretty bad bruises, so you have to try not to get too carried away.