As a submissions editor, one of the most important considerations I have to think about in deciding whether or not to recommend your MS for a publishing offer is the cost of getting your MS into publishable condition. Copy editing costs money (and time), so if your MS is almost entirely error-free and adheres to the publisher's style guidelines when it's submitted, then your chances of being offered a deal are better than if the publisher has to put your MS through the standard editing process. And even if you're a self publisher, the more error-free your book is, the more likely readers are to take it seriously.
“Accidently” is an increasingly uncommon spelling of “accidentally”. Use “accidentally”.
Breath = noun vs. breathe = verb (ex. "You need to breathe, so take a breath!")
Canvas = a kind of cloth vs. canvass = to search or to solicit
Compliment = a nice comment vs. complement = to go well with
Cavalry = soldiers on horses, vs. Calvary = the hill where Christ died
Desert = an arid, often sandy landscape vs. dessert = a sugary treat
Discreet = done with discretion, avoiding the public eye vs. discrete = individual, separate
Fiancé = a groom-to-be vs. fiancée = a bride-to-be
Hanged vs. hung, with regard to people: people are hanged, pictures are hung (well, people can be hung, too, but this mostly just applies to the Romance genre)
Horde = an army vs. hoard = a stockpile, or the act of stockpiling (ex."The Viking horde buried its hoard near the shore.")
"I could care less" = you do care somewhat vs. "I couldn't care less" = you don't care at all
Lay vs. Lie:
Lay (present tense) = to place an object (A trick for remembering: “You lay a tray.”)
Lie (present tense) = to recline
Laying (gerund) = the ongoing action placing an object (ex. “She’s laying down mousetraps.”)
Lying (gerund) = the ongoing act of reclining (ex. “There’s a mousetrap lying in the corner.”)
Lay (past tense of lie) = to have reclined (ex. “Did you lay down yesterday?”)
Laid (past tense of lay) = to have placed an object (ex. “She laid the mousetrap in the corner.”)
Lain (past participle of lie) = to have had reclined (ex. “You had lain down for a nap.”)
Laid (past participle of lay) = to have had placed an object (ex. “She had laid the mousetrap in the corner.”)
Lied = to have told a lie
Lead = the present tense of the verb "to lead", also the metal vs. led = the past tense of the verb "to lead"
Lightning = a bolt of electricity vs. lightening = making something less heavy
"Netflix and chill" is a euphemism for having sex. It does not literally mean to watch movies and hang out. No exceptions! For whatever reason, I almost only ever see this error in "Sweet & Wholesome" content.
Ordinance = a rule/law vs. ordnance = explosive munition
"Per se", not "per say"
Pistol = a handgun with a non-revolving magazine vs. revolver = a pistol (usually) with a revolving cylinder
“Publically” is an increasingly uncommon spelling of “publicly”. Use “publicly”.
Sheathe = to put a blade in a sheath vs. sheath = an object in which a blade is stored (“Sheathe your word in its sheath.”)
Sí = Spanish for "yes" vs. si = Spanish for "if"
Stylus = a writing implement, such as a pen or pencil vs. stylist = someone who advises on wardrobe, hair, makeup, etc.
Shutter = exterior window cover vs. shudder = to tremble/shake
Tenets = articles of purpose, often for a corporation vs. tenants: building and housing renters
Vile = disgusting vs. vial = a small bottle or test tube
Waiver = permission to disregard a rule vs. waver = to vacilate, to balk
Who's = who is vs. whose = possessive form of who (ex. “Whose Who’s Who is this?”)
Who = the subject of a sentence, will usually come directly before a verb or adverb vs. whom = the object of a verb or preposition
Yeah = modern informal way of saying "yes", vs. yea = old-fashioned way of saying "yes", sounds like "yay"