I'm the one behind the camera, so my tips are what I give to my models. It's really all about how relaxed you feel. Find a photographer that makes you comfortable, makes you laugh (a genuine laugh is about as sexy as it gets on film), and understands posing.
As the model, focus on your eyes and maintain good posture, especially through the shoulders. If you concentrate on making bedroom eyes that go through the back of the camera, the rest of your expression and pose will naturally relax and look amazing. Also, grab a mirror, and practice posing yourself. A glass of wine or two makes this alot more fun.
Try peeking from around a curtain with come hither eyes, posing in front of a bright window with your hands through your hair, laying across a bed or the floor, and especially the pin up style. Check out Gil Elvgren, and see what kind of poses his models do.
Also play with facial expressions. Look over your shoulder for a tight shot, throw your head back and laugh while your hands love your curves, crawl towards the camera, pamper yourself in the mirror, and so on.
Another thing to remember, you don't need to look at the camera EVERY time. Sometimes, it's sexier to capture a mood or a moment that doesn't feel posed, and it offers you a chance to break away from the camera and get relaxed again. When you smile, take a deep breath and exhale into your smile. If you don't smile, part your lips slightly to give your face a smoky expression, and bite your lip or fingertip for a flirty expression.
I'm so excited for you! Just have fun, and remember that its for the one you love, so if pose for him, you'll look amazing!