You're doing great so far! As @ambiguity mentioned, everyone has its tastes, so I'd suggest to look for many references of people that you find attractive, and pick up what they all have in common, so then you will be able to apply those attributes to your characters. Also, pay close atention to the face and expression you want (this, again, depends on what you like), because that make a huge difference. Then, the hands may need a bit of extra work. Her right hand seems like it's pressing on a table. The hands can add ton of expression. Try relaxing that hand, even something as simple as make the fingers wrap around the volume of that leg a bit more. I would go a little further and try different positions for the entire arm and the shoulder (can be subtle and still make a lot of change in the general feeling). And her left hand is making a posing that throws me off. Try to do that with your own hands and will see what I'm talking about. Another thing to have in mind is the interaction between the bikini and the body, that at the moment, doesn't seem to press the skin.

Based on your line style I would guess you're familiar with him, but if not, you should check out Frank Cho's work as an example.

If you want to make her naked she would look more real if her breasts would fall more naturally (especially the front breast). In case you will dress her up, it's ok since there are bras that could make breasts look this way. Sometimes a bit less perfect is more attractive because it gives character and real-feel. I hope this helps. BKG: what are you going for? Sports car, beach, surfer-board,...

I feel like the stand out issue for me is that it looks like you are spending a lot of time on making the anatomy 'correct' but not so much time on shape design and flow. The result is almost more mannequin like than organic. There are a lot of good videos out there on silhouetting and working on that might help some. Also look at the way gravity acts on the body, particularly for the breasts in this piece, and many really good figure drawing teachers talk about exaggerating the pose as well which can help. Also have a look into the Riley Method as it's a good way to break out of slaving at anatomy (important as correct anatomy is) and finding more gestural flow, at least for me anyway as I have suffered with the same problem you're having.

For the background, since she's already in a bikini, maybe at the beach (?). Some guys at the back trying to take a peak, but she's only showing her cherries to the viewer. As for how to make her more attractive, i think @ambigiuity suggestion is very good. Since eyes are an amazing tool for expressions, You can give her a more inviting eyes and a smirk that tells the viewer "only for you sweety". It'll fit well with the background idea too. anyways that's my 2 cents. i'm still working on expressions myself so take what I said with a grain of salt but I hope it helps in some way. Also, one of my favorite manga artist, Naoki Urasawa, said in an interview that he draws the eyebrows first to draw better expressions. He mentions It's probably not for everybody but idk maybe maybe you wanna try his technique for a spin hahaha. i'm gonna try that soon. anyways good luck. Overall this looks very good ;D.

My suggestion would be to focus less on musculature and more on gesture. For example, if perhaps you eliminated the small bump of the lat muscle as it connects to the lower back, it might create a more flowing gesture and possibly capture essence of the pose. I imagine a RIta Hayworth type movie poster pose here. Good luck!

A less transparent bikini, it leaves more to the imagination...just kidding, great proportions and yeah, just go for the hair and see if it works, and you said pin up style right? Aren't the colors a bit different when you do it in that style, a bit vintage style? Or am I wrong?

That's a bit of a tough question to answer because it's pretty subjective. We're all human, so there will of course be some overlap, but I think it's better to firstly ask yourself what you find attractive, and then brainstorm ideas on how to get closer to those things. One thing I will say, though, is that with the exception of her eyebrows, her face isn't very expressive. As a result, I don't get a sense for how she feels about this situation. Perhaps this is why you feel it's "losing character", because she's not really expressing an emotion that we can relate to. If you look at Gil Elvgren's pinups, a lot of them are either expressing embarrassment in their face over their predicaments, or giving an alluring smile to the viewer so you know that they are purposefully trying to seduce you, or sometimes they are completely engrossed with other elements in the scene and reacting to that instead. Whatever the case, it always looks like they are thinking about something. Something Glenn Keane said once was that a big game changer for him was when he learned to animate what Tarzan was thinking, and not what he was doing. I think this is a great hint for all artists into how to make something feel more human, and maybe more "attractive" as a result.

Honestly you're a far better artist than I am but I would just leave more to imagination. You can draw a good looking female body but theres a lot more that goes into it. I used to like the pin up style skateboard decks that the company hook-ups used to paint because I think they manage to fit a lot of character into something super sexualized. Some definitely ere's on the side of pornographic but you just gotta find some similar artwork to yours and get an idea from there. I think that's a good place to start. Also pinterest and reddit have a ton of images you can get inspired from. Hope I helped.