>>2800317You will very quickly run out of other ways to write "Nipple", "Breast", and "Vagina".
Keep in mind that the various synonyms all come with a different connotation and cannot simply be exchanged with one another freely. (A word like "Breast" or "Mound" has a different connotation than "Tit" or "Milker".)
My method is to start with the more 'medical' terms first and slowly work your way to the very lewd later on.
In your nude modeling scenario, maybe the girl doesn't start out enjoying it and so her naked body is mostly described in artistic and literal terms, but as she begins to enjoy the exposure more and more, the heroine (and the narrator) start to use more expressly sexual words.
Consider
>>2800342 's advice, a slow build definitely makes the payoff more satisfying, but readers will always want something up front as a sampler of what you're building to. I often write stories in a 'Metroid' style, with a spicy scene to show off the potential and then working up from a regular situation afterwards.
Though, this advice applies more to long-form stories. If you're just doing a quick fic then there's no reason to do a slow build-up.
Like any story, a helpful tip is to start as close to the end of the story as it makes sense to do so. Don't write her hearing about the modeling gig, then thinking about it, then signing up, then waiting for the day to come; Start off with her being told to undress and then back-fill to earlier. Or better yet, have her naked behind a curtain trying to work up the courage to walk out (I know this is one of those "Yep, that's me. You're probably wondering how I got into this situation" moments, but as long as you don't act too effervescent about it this sort of intro can still work.)
