It's basically what the title says, I'm going to give you some tips when writing smut (I'm bored so I'm doing this lol)

#1)know what the fuck you're doing- basically, have an idea or plan for smut. Like, what occurs? If they do occur, are they reasonable. You can't just go from two people making love in their bedroom to an orgy in a sex club in two sentences. That kind of thing is only ok in crack smut

#2) know terminology- basically think and envision the smut in your head while you write it. If someone in the comments asks what position the characters are in because they couldn't figure it out from your confusing writing, how will you help them if you don't know the name of the position? By terminology, I mean, know the name of sex positions and sex acts

#3)be illiterate-basically use good grammar and spelling

#4)sane, safe and consent- basically make sure what you write is sane, safe and your characters are consenting to it, doesn't matter if it's just regular sex or something really kinky

Now let's cover the 3 levels of sex

-low
-medium
-high
They go something like this

Low-
The two lovers celebrated by taking each other to the bed, where they spent all night there. The sheets wrapped around their torsos, drunk in what they were doing, and on their love

Medium
The boy sets himself between his lovers legs, who spread their legs wider to allow the boy better access to what he wants. The boy lines up and pushes in until his hips are flush with his lovers

High-
The boy rubs the tip of his cock against his lovers swollen pussy lips. Teasing them until they can no longer take it and whine for the boy to fuck them. The boy complies, pushing in and burring his cock deep inside his lovers pussy.

It's not a good idea to switch between the levels in the same chapter unless it's done gradually

Now on to: cum vs come
I've seen people use these words interchangeably in fanfics but some people often get confused on the difference between the two
To set the record straight

Coming is orgasming and cum is what is released when someone orgasms (basically, coming is the action, cum is the fluid)

Another tip is don't just use the words penis or vagina, because although you're correct, but it's not very hot. There are some words you probably wanna stay away from like manhood. Some good words to use are throbbing, pulsating, quivering, cavern, tunnel, channel

Also please never use the word turgid unless it's crack smut

There are good reactions words too, examples-
Shivers

Shudders

Trembles

Quivers

Quakes

Shakes

Gasps

Moans

Groans

Jolts

Jerks

Lurches

Startles

Pants

Huffs

Gulps

Cries out

Melts

Bites back a moan

Breath hitches

Babbling/sputtering

Collapsing

Knees buckling

Swallowing hard

Going limp

See stars

Makes a strangled noise

Inhales (combine with an adverb i.e "he inhaled sharply")

Exhales

Skin prickles

Brain short-circuits or stops functioning

Sweating (there's loads to be done with sweat: the musky smell of it, tasting the saltiness of it, seeing a lover coated in a thin sheen of it, having it slick their bodies, etc.)

Flushing (Flushing tends to happen in fleshy and sensitive areas. Armpits, cheeks, neck, ears, chest, genitals, and whole-body flushes for maximum effect)

Eyes roll back

Clenches

Is stunned

Arch back/hips

Some good adverbs are-
Shakily

Heatedly

Desperately

Incoherently

Roughly

Raggedly

Headily

Readily

In a Needy way

Deeply

Breathily

Noisily

Loudly

Heavily

Dangerously

Seductively

Languidly

Lazily

Sensually

Silkily

Oily

Hungrily

Sinfully

Darkly

Warmly

Softly

Gently

Tenderly

Harshly

Lusciously

Quickly

Slowly

Frantically

Wantonly

Sexy words to use instead of said (said is dead)-
Purred

Cooed

Murmured

Whispered

Stuttered

Breathed

Rasped

Cried out

Begged

Muttered

Growled

Grunted

Husked

Howled

Keened

Mewled

Choked

Sobbed (dub-con warnings; use with caution)

Whimpered

Blurted

Teased

Pleaded

Sinking to their knees

Licking

Biting

Nipping

Pressing foreheads together

Shoving a hand between someone's legs

Shoving your hips together

Pinning their wrists

Caress

Wink

Wet/lick lips

Hike a skirt up/ruck a shirt up

Stroke (skin, hair, genitals, etc.)

(when one character is pressed against a wall) A does something, and B slams/throws their head back into the wall in reaction.

Undoing buttons/zips with their teeth

Splay hands across someone's chest or lower back

Rake nails across skin/through hair

Hooking a leg around someone's waist

Knee between thighs

Biting collarbones/hip bones/ribs (the bones that tend to protrude beneath the skin and draw it taut)

Sucking neck skin into the mouth

Cupping their cheeks

Grasping their chin and tilting it up/down

Placing a finger against their lips

Letting breath tickle their ears

Digging your nails in

Tugging on earlobes with teeth

Push their hair back/card through it/rake through it

Hair pulling

Lips brushing ears

Ghosting over their neck with fingers/lips

Running fingers lightly over someone's palm or wrist

Hip grinding/rutting/thrusting/rolling/shifting/rocking together

Dirty Talk

Nuzzle

Tease/torture/torment

Some generally accepted slang terms are

Clit

G-spot

Cock

Dick

Prick and Fanny for the Anglophiles (penis and vagina)

Slit (male and female)

Entrance

Emphasis
Basically if you wanna emphasize words, I recommend making the letters all uppercase or bold (do both to really emphasize the word)
Examples:
He was really big

He was REALLY big

He was really big

He was REALLY big

Now for tips on writing Male x Male

For male x male, LUBE IS A MUST, you can't just shove a dick in an asshole and expect it to fit. Unlike a vagina, an asshole can't produce its own lube, plus it'll be painful for both characters, wether their receiving or giving

I don't exactly have any tips for writing female x female. Basically all the characters are doing is either fingering and/or rimming their partner or rubbing their clits together

I hope this helped. If you want me to, feel free to private message me and have me look over and give my opinion on any smut you write, bye!