Hi, I have some suggestions that __might__ improve your generations.
First and foremost, using a good model is extremely important. If you don't have other preferences, you can try grapefruit: https://civitai.com/models/24383/grapefruit-hentai-model (yes, that means you should set up stable diffusion on your computer.)
I think your negatives are not strong enough. I personally use bad-artist: https://huggingface.co/nick-x-hacker/bad-artist and bad-image-v2-39000: https://huggingface.co/Xynon/models/blob/main/experimentals/TI/bad-image-v2-39000.pt . In my experience, strong negative can give more depth to your pictures.
Also, you might want to consider to always have some background in your prompt. I find having background generally improves the overall lighting of the picture, so it is less "flat".
Anyways, good luck on your generations. Always looking forward to more Hatsune Miku pics. :)