Making SD do precisely what you want with photorealism work means finding unambiguous words. You try, essentially, to leave SD no wiggle room to interpret what you want.

Here are some keywords (only tested on female models) I developed across 10,000 renders and god knows how much time Googling for phrases. These are words that have a verified impact in SD 1.5 and k-euler – for every keyword in this, I rendered a Txt2img prompt across the same 8 incrementing seeds at 512x512, 16 steps, and a CFG of 7.5, and compared the difference to the original prompt. What this doesn't include are the untold numbers of words that did nothing :)

One tip up front: even just mentioning a body feature changes it in Img2Img. That's why "big cheekbones" works. In fact, in my testing, "cheekbones" produces the exact same result. Try just mentioning the quality you have in mind: almost everything (besides certain things, like the nose) can be changed, though maybe not in the way you want. "Lips" will add comical clown lips to the photo. "Eyes" will add vivid hues to the eyes. Adding "Hips" will make the hips more defined or prominent in a photo, for instance. And "small hips" does just the same :(

(As an aside, that's a part of how I tested: if a body part changed in most seeds, without my prompt including that body part, the keyword is effective)

General

• People: I like vague people keywords, to let SD be creative for me. "Supermodel" renders a beautiful face, but is generally rail thin. "Model" is too vague. Try "blonde bombshell"
• "Spray tan" is a very strong keyword, and a healing tool. SD will spend much more attention to the skin of a model, evening it out – very useful in img2img rounds with a lot of noise. May also make the skin shiny, which is useful in some bright settings.
• "Onlyfans" as a keyword does a lot. Try using it in different places ("onlyfans outfit"). "Gonewild" produces naked, but unattractive, people – it can help in img2img.

Posing

Do it in Photoshop. Seriously. Few poses have single word descriptors, and even fewer look the same for everyone. That means SD will not be able to reliably generate photos. "Jumping" is a classic hard one. Tips all the same:

• "[name] in lordosis pose" is not a strong keyword, and will reduce render quality. But it gives you a sexy "looking over back" pose, which can let you see the back of characters! You can then restore the quality in img2img.
• Single word, same pose for everyone... what has that? Well, yoga. "[name] in padmasana pose" is an extremely strong prompt that will have every render in a crossed-legs meditation.
  • Unfortunately it seems SD has a lot of confusion about most other Yoga poses, but it does have many faint connections. Just be patient with the results and keep trying.
• What else has unique names for identical positions? Ballet! Try "arabesque ballet pose" (SD gets confused without "ballet")
  • SD can only barely work with these. You won't be able to adjust them much.

Or just use Photoshop :)

Body

• Hair: for silly enormous hair, try "huge rapunzel hair." It doesn't do much in Text2Img, but makes Img2Img accept absurd, impossible hair at high CFG's, turning your shitty drawing into terrifying reality. How impossible? How enormous? This much.
• Add "flowing" and "windblown" for even more enormous hair.
• Terms like "straightened" and "curly" have a strong effect on hair.
• I couldn't find a way to render shorter people :( "short" does nothing. "Midget" does not change height, but does give people bizarre proportions.
• "Giantess," though not a strong keyword, does make the character taller. Look at this before and after - I'm seriously impressed. Add "stilettos" and make your character's head soar beyond any size of SD render.
  • Note that 1/5 of your photos will turn into superheroes. Nothing to be done: adding "heroine" or "superhero" to the negative prompt removes the normal effect too :(
• "Curvy" adds dramatic curves. Combining curvy with "corset" basically immediately produces a porno bodyshape. "Thick" is 50/50 between truly big women and attractive thickness. "Hourglass figure" has a weak, but noticeable, effect.
  • You can then remove the corset in img2img to just have a wildly-proportioned person. Img2img is not aware of real curves vs corset-powered ones.
• "PAWG" as either a noun ("a PAWG") or an adjective ("a PAWG woman") reliably generates HUGE butts and tiny waists, and also has poses associated with it. Extremely strong keyword!
• "Thicc" also produces huge butts, though adds weight up top as well. "Thicc PAWG" produces some sturdy gals. "Bottomheavy" only has a small effect, but can sometimes radically change pose. "Zaftig" and "BBL" have no effect, "curvaceous" has only a small effect.
• "Slimthick" does... something? Unclear.
• Like ripped girls? Just do "ifbb" – add "muscular" to get a woman who can rip your arm off.
• Even just mentioning "hips" tends to produce broad ones. No result from "breeding," "wide," or "childbearing" hips.
• "Midriff" and "Exposed midriff" have a strong effect. Add adjectives like "toned" or "muscular" in img2img, after it's been exposed.
• "Waspwaist" won't actually make most waists smaller (use "corset" for that), but does tend to add fun decorations around the waist on most outfits!

Breasts

Small: No clue. Avoid "tiny breasts" & "small breasts," (just makes them bigger! see earlier), "petite", "flatchested," "bugbites" (just makes bees appear), and "mastectomy" (I tried).

Adding "cleavage" to negative prompts helps, but does not work with "busty" et al.

Big: There are likewise not many good words for big breasts. I tend to just use "busty," a lot of img2img rounds, and some Photoshop to help. Img2img interprets "busty" as bustier than the image, and keeps scaling it up for you. There is a natural limit, though, after which you'll need photoshop.

• Across 10 tests, "extremely busty" and "very busty" had literally 0 impact to size compared to "busty" (it may in img2img, though)
• Specifying cup size, like "DD-cup breasts," had no noticeable impact for any cup size. They changed the image a lot though
• "Cleavage" is also an extremely strong keyword.
• "Stacked" can help a tiny amount with bustiness. "Buxom" tends to make women on the plumper side. "Braless" will make breasts hang more naturally, but also become smaller. You can also go full tilt and use "Scoreland model" as the subject (the only big breast mag I could find in SD).

Clothing

• "Cinched" will make any outfit cling to the waist. This will also force the clothing to contain the waist – making it a neat trick to get rid of midriffs in img2img.
• "Revealing" and "lowcut" both work well.
• However, "Plunging neckline" is the atom bomb of sexiness. Make outfits reveal dumb amounts of cleavage! Also try "sweetheart neckline" and "vneckline" (other spelling combos don't work as well), or "cutout"
• Note the "neckline" – "plunging" on its own, without "neckline", only works with dresses. With it, you can sexify shirts, tanktops, whatever!
• "Strappy" is a fun word to improve anything. I also like adding "sophisticated" and "elegant" to a precise outfit (a "sophisticated pink dress")
• "Pushup" will literally make breasts larger.
• "Halter top" only works like 1/5 times. Instead do "halter neckline top, exposed midriff." Avoid "halterneck"

More sexy clothing ideas:

Corset, cinched corset, cinched boned corset, bodystocking, romper, catsuit, minidress, ruched minidress, ruched bodycon minidress, slit minidress, corselet, loose top, two-piece [type of outfit], bodice, peplum dress, flared peplum dress, a-line dress, asymmetrical dress, off-the-shoulder dress, sweater dress, athleisure (or lululemon, or gymshark), compression suit, crisscross halter neckline top, cling dress, bodysuit, compression suit

• Feeling uninspired? Just give it a designer. "wearing gucci outfit and loubuiton stilettos"
• Feeling even more uninspired? "Sexy outfit" usually does fine – just add "bikini" to negatives.
• Add latex or rubber to any of the above. PVC tends to be hit or miss.
• Stockings and garters stick around in Img2img if you have them in image and specify them in your prompt. But they're really hard to get txt2img to render correctly.
• "Zettai ryoiki" works very well.
• Add "colorful" before the outfit to make it bright and exciting.
• You can give SD more control by specifying only some single quality of the clothing, like "waist trainer outfit"
• Shoes: SD sucks at them. "Stiletto pumps" kinda works. "Knee high boots" and "thigh high boots" both are very strong, just add a fabric like "leather" to make it stick.
• "Chunky heel boots" works a bit better, I believe simply because it's thicker.

Close-up face changes

These only become possible when you're doing an extremely tight zoom on someone's face. That happens with e.g. "Close-up head portrait of [person]"

• Face shape: "cherubic" and "chiseled". Being precise with face shape is hard. I recommend Photoshop. But those two will move your Photorealistic model in either a more girly, younger look, or a more smoky, model look.
• Makeup: if you specify any color of makeup ("red lips!"), that color will appear in other parts of the image. Yuck. But if you want the absolute caked-on porn look, instead try "makeup by twistys." This will also make the character face the camera. Use it multiple times (or emphasize) for thicker makeup. For extreme pancake makeup, try "contouring runway makeup by twistys". If your prompt is long, make sure to emphasize this so it doesn't get drowned out.
• Want to remove makeup? Use "bareface" and add negative keywords like "makeup, lipstick."
• "Lash extensions" and "mascara" will both produce huge, fan-like lashes. Here's a before/after of adding them and eyeliner https://imgur.com/a/TAdCIT7. Did SD just become the best cosmetic surgery app?
• "Microblading eyebrows" makes eyebrows symmetrical, and... different. Basically the only way to affect the eyebrows I've found. (It will also turn the occasional render into a bunch of eyebrows. Add "before, after, before&after" to negatives). "Microbladed," "microblade," "brows," and "micropigmentation" do nothing.
• Nose: I believe specifying nose type with img2img or text2img is just not possible. Inpainting understands nose types, though, e.g. "caucasian woman aquiline nose"
• Cheekbones: just use "cheekbones." "Gaunt" and "sunken" will both affect this, but only minutely. Requires many Img2Img cycles to actually be noticeable, but can produce some fucking insane cheeks if you stay with it. This horrifying fleshy skull was done through Img2img, but it took nearly 200 rounds of "gaunt" "skeletal" "hollow" and more. Just use Photoshop.
• "Ducklips" will provide big pouting lips. Note that this keyword makes smiling all but impossible.

Misc.

"Crowded" will add (a lot) of other, terribly-rendered people to a setting. Add a short focus to make them blurry and acceptable, e.g. "f2.8 short focus bokeh"

Outdoors works best for our monkey brains to get past uncanny valley. This is 90% of making a good photorealistic image. Tell SD a specific location with a short name, like DTLA, and prepend it with the time of day to get consistent backdrops: "sunset DTLA." Be sure to tell SD about the time in the model's lighting, too. Here's a non-cherry picked example from txt2img:

Nikon 4k fashion photo of sunset lighting from left supermodel looking into camera walking in sunset DTLA

I cannot recommend enough looking up lighting terms. They're usually quite specific and unique, and make SD add a lot of life to your scenes.

Prompt ideas:

• "Telephoto paparazzi photo of [subject] walking in [location]" (use 384x512 to avoid heads getting cropped)
• "Olympics stadium telephoto photo of [subject]"
• "Stadium telephoto photo of [subject] performing on stage, solo performance, theatrical fog, red and blue lighting"
• "White House press photo of [subject] in [DC location]"
• "Candid photo of [subject] [verbing] in [location]."
• "Night candid harsh flash photo of [subject] [verbing] in [location]. Extreme shadows."

Keep in mind that SD can be searched in other languages too. I recommend trying to find slang, which is usually quite precise.