A good photographer will probably have some idea of what to do. Show the photographer and your wife some images you like just to give them an idea. Try not to do too much as in too much wardrobe, too many ideas, too many specifics, etc. Does your wife have much experience in front of a camera? You may not get what you are thinking of but you will probably get a couple you really like.
Just as an example you take the shot of the girl looking back over her shoulder. Classic "boudoir" kind of pose. Get her legs in front of her and maybe she does a look down at the sand before looking back and smiling at you with this little come hither expression. Just play with stuff like that.
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I guess this kind of speaks for itself. Play around in the dunes with how much she shows off and the way she looks at the camera.
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Searching Vintage photos for examples is a good idea because they aren't too explicit and with minimal lighting and setup. And remember it's romantic so keep it light.
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And then remember you're at the beach so bring something lightweight and get it wet. "Boyfriend shirts" are great for this. Wet sand, wet shirt about to fall off, you get the idea. Bring a bucket.

And yeah, you can imply a lot of fun stuff within our genre. I shot that last one years ago at Fred's place. There's a jungle girl you'd like to see.

Maybe make a series of 3-5 so you can collage them in one frame for kind of a little story.
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So anyhow there's my two cents worth and it's always subject to being improved upon. Sounds like a lot of fun. Oh, and you better keep her.

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It's a dirty job but I got to do it for 27 years. Thank you.