If you've never posed with a female model before, don't worry about being nervous, that all comes with the territory. Don't be afraid to speak to your female modeling partner. The better you get to know her before and during the shoot, the better your photos will turn out and the more comfortable you'll be while posing.
There's nothing wrong with asking if it's okay to put your hand somewhere, like her thigh or around her waist. If the model you're posing with is already experienced, she won't even give it a second thought. Ask her about her modeling experiences and if she's used to modeling with a male model. That will help you learn her comfort zone.
Avoid looking like you're posing. Couple shots with a male and female model should look like the photographer captured the moment without the two of you being aware, unless you're looking at the camera of course. Look into her eyes and hold her like she's the woman of your dreams.
If there's a height difference (although that's highly unlikely, since those type of shoots make sure the models are both within the same height range) try to do poses that won't make her look like a dwarf compared to you.
At a loss for poses? Start experimenting. Sometimes action shots look great if done the right way. Try leading her by the hand and walking towards the camera. Think of the cute little gestures guys do to their girlfriends: kissing her hand, holding her chin in your fingers, throwing your arms around her, etc. Even the smallest gestures can carry the picture.
At the same time, don't be afraid to look at the camera. One way to capture a variety of looks with limited poses can be done as follows:
1) You looking at the camera while the she is looking somewhere else:
2) You looking at her while she's looking at/towards the camera:
3) Both of you looking at each other:
4) Both of you looking away from the camera:
5) Both of you looking at the camera:
6) You looking away while she looks at the camera:
Don't be afraid to take the lead and at the same time, don't be afraid to let your female partner switch things up and take the lead from you. When you're in charge, make sure you are in the forefront of the picture with your female partner a little behind you. This illustrates the perfect balance of the male taking charge with the female following behind, but not in a way that she is beneath the male model.
Examples of male model taking the lead: