I wanted a lora for creating mermaid/trumpet-like silhouettes, but not just for dresses. I wanted it to really get the silhouette right, which I always found looks absolutely regal, so it's actually more versatile than you might think, it can do mage robes, kimono, pants, loincloths, and, of course, dresses. By default the lora leans female, but actually if you use it along with Gender Slider and/or femboys sdxl loras it can perfectly fine do men.
I also highly recommend describing the background you want as well, as otherwise it has a tendency towards plain or forest backgrounds for some reason, as well as using intricate background as a tag if you don't want character sheets. You can have a look at the prompts for my images for examples. Tested it mostly with Plant Milk Hemp II and it works amazing thus far.
The trigger word is s1lυ3tt35 but I recommend also using some secondary trigger words for more specific effects:
f1@r3 = flares the clothing

f3@r3d = normally this was supposed to make them be made of feathers, but instead it generally works great to exaggerate the silhouette or bring it out more if it's not coming out strong enough.

3mβr = embroidery and embellishments

3xag3r8d = normally was supposed to make the silhouette more exaggerated, but for some reason this one doesn't really seem to work. You can probably skip this one.

Pυδδ13 = makes them pool on the floor more.

Added with V2:

gilded = metallic gilt-like patterns,

stylistique= more fashionable and stylish/avant-garde/bold designs,

embroiderment(yes, I know that's not a real word, I did it on purpose because I wanted it to sorta understand what I meant while not overlapping with so much of its training data as if I had used embroidery or embroidered, but that's basically what it means),

lace = self-explanatory, great for wedding dresses.

It also helps to have something like standing or sitting, as well as angle words like frontal/profile/from behind in your prompt.

Update Notes for V2:
Better embroidery and ornamentation.