More an assortment of Flutterrape culture that's built up over the years than actual rules.
Although you should probably memorise all of them, just to be safe.

Rule #1: >rape
Rule #2: Because magic
Rule #3: Lee Sin is the best champion of the game.
Rule #4: If you're not providing content, take your trip off.
Rule #5: ...And your name too.
Rule #6: Nebby is a butt.
Rule #7: Rarity has an affinity for alcohol.
Rule #8: [MOTHER] is watching.
Rule #9: Rainbow Dash is a bro.
Rule #10: If Rainbow Dash has feelings for Anon, Anon must be completely clueless about the situation. (The Rainbro Postulate)
Rule #11: Pinkie Pie must throw Anon a party.
Rule #12: The Circlejerk is a graveyard.
Rule #13: Anon must black-out at some point.
Rule #14: Hot Monkey Dick is comparable to Equestrian Horsecock in size. 
Rule #15: Human stamina makes Anon a superior lover to stallions.
(Rules #14 & #15 are together known as the Sexual Superiority Theorem)
Rule #16: U wan sum fuk? 
Rule #17: You gotta earn the right to Avatar-fag, and if you have to ask you haven't earned it.
Rule #18: Twilight will do anything for science.
Rule #19: Twilight will be interested in studying Anon...for science.
Rule #20: Twilight may or may not be a gassy pony, but Fart-Anon is still a fuck.
Rule #21: Applejack is frustrating as fuck to write well.
Rule #22: You are less manly than Theseus.
Rule #23: You are more manly than Lasagna.
Rule #24: All Anon's are in some way a self-insert.
Rule #25: Anon will arrive mysteriously in the Everfree.
Rule #26: Fluttershy collects Anon's underwear.
Rule #27: Lyra has a human and/or hand fetish. 
Rule #28 Flutterpriest is in fact a sixteen year old girl and has been for years
Rule #29 No filly fiddling
Rule #30 Exists to abolish rule #29
Rule #31 Shit. Shower. Shave. In that order
Rule #32 Blame the pony who raped you 
Rule #33 Acknowledge that it is always Fluttershys fault
(#32 and #33 is known as the >Fucking Fluttershy clause)
Rule #34 We don't fuck horses
Rule #35 Pinkie rapes you without even being in the story
Rule #36 No one must know you exist on this thread
Rule #37 Lumberjack Anon is never raped, only harassed
Rule #38 Requests are encouraged, but not expected to be fulfilled
Rule #39 There are three known writers who will fulfill your requests if summoned correctly
Rule #40 Slasher fights for your right to live
Rule #41 The CMC try to get their cutie mark in human fucking, it never works
Rule #42 Always have your special comfort blankie or plushie nearby
Rule #43 UV provides the nightmare fuel
Rule #44 We are not liable for wishing to commit suicide after reading a story
(#44 protects us from #43 and #42 works to prevent #44 from being applicable. This is the UV chain)
Rule #45 >Bump
Rule #46 Puns, cats, and dogs all summon horrible things. Refrain from using them.
Rule #47 Jchallo has never done drugs and is never allowed to
Rule #48 That writer doesn't exist but is a decoy played by another writer
Rule #49 The only esc-[REDACTED]
Rule #49 The ride never ends.
Rule #50 Drama. Drama never changes
Rule #51 Circlejerk stories are just that and mustn't be done
Rule #52 Fucking Alicorn's
Rule #53 Cadance is her own loophole, allowing her to rape you
Rule #54 Don't let the ponies team up, you won't survive
Rule #55 The Anal Pulverizer is named for a reason
Rule #56 Chasity belts
Rule #57 Apple horse is stronger than you so don't fight
Rule #58 Diamond Tiara will buy you
Rule #59 Celestia and Luna can use the law to force you
Rule #60 If you wake up with one in the bed, it's too late.
(Rules 57-60 are known as the definite rape clauses)
Rule #61 You can't, in fact, rape the willing
Rule #62 Nebulus is the hero we need, but don't deserve.
Rule #63 Zecora has a potion for what ails you.
Rule #64 All Equestrian drugs and poisons work on Anon, different species be damned.
Rule #65 Anon may or may not be resistant to magic.
Rule #66 "The Stare" can and will be used in times for desperate rape.
Rule #67 Changelings were born for this thread.
Rule #68 All Cutie Mark talents can easily be swapped for raping talents.
Rule #69 ...Heh 69
Rule #70 Your waifu a rapist.
Rule #71 Trixie will always be Tsundere for Anon.
Rule #72 Go ahead and tattle, no one will believe you.
Rule #73 Using another pony for protection only delays the inevitable.
Rule #74 Sexual favors are the default currency in Ponyville.
Rule #75 Wearing clothes other than those for formal occasions is considered weird and unnatural.
Rule #76 When in doubt, assume Brownee is in the Hospital.
Rule #77 No matter how many skills Anon has, he will eventually need to ask a pony for a favor.
Rule #78 Equestrian alcohol is for lightweights.
Rule #79 Princess Luna is always spying on your dreams.
Rule #80 Tom is best rock.
Rule #81 Anon's mere presence can shatter married relationships.
Rule #82 Griffon's are the only means of acquiring meat.
Rule #83 You can run, but you can't hide.
Rule #84 Adoption is not an option.
Rule #85 Answering the door is never a good idea.
Rule #86 A human's favorite food is always bananas.
Rule #87 If Discord is involved, give up; it'll hurt less.
Rule #88 Locking up your house is merely a formality at this point.
Rule #89 Trust no one.
Rule #90 Pony stupidity can used to your advantage if done carefully.
Rule #91 Your story idea has been done before, get over it.
Rule #92 Humans can't get ponies pregnant.
Rule #93 Magic can do anything.
(Rules #92 & 93 are considered the "Satyr Paradox")
Rule #94 Every pony has its own cereal. 
Rule #95 Estrus = Easy Mode
Rule #96 If at first they don't succeed, cry cry again.
Rule #97 Anon may only bring to Equestria whatever was in his pockets and/or hands at the time.
Rule #98 Common sense is considered "optional" in Equestria.
Rule #99 If Anon's fetish is revealed, he MUST submit to whoever offers it.
Rule #100 Don't forget, you're here forever.
Rule #101 Rarity is the only living being in Equestria that knows how to create human clothes.