A lot of alot:
If you like to indicate a plenty of something then better do it by placing a space between ‘a’ and ‘lot’ so the proper version is ‘a lot’ and never alot. This is one of the commonly repeated mistakes which people tend to ignore despite warnings from spell-check.
Lost over lose or loose:
When people mix up "lose" and "loose," it's usually just because they're spelled so similarly. They know their definitions are completely different.
According to Merriam-Webster, "lose" is a verb that means "to be unable to find (something or someone), to fail to win (a game, contest, etc.), or to fail to keep or hold (something wanted or valued)." It's like losing your keys or losing a football match.
"Loose" is an adjective that means "not tightly fastened, attached, or held," like loose clothing or a loose tooth.
It's vs. Its:
Normally, an apostrophe symbolizes possession. As in, "I took the dog's bone." But because apostrophes also usually replace omitted letters like "don't" the "it's" v. "its" decision gets complicated.
Use "its" as the possessive pronoun: "I took its bone." For the shortened version of "it is" use the version with the apostrophe. As in, "it's raining.
Less vs. Fewer:
You know the checkout aisle in the grocery store that says "10 Items or Less"? That's actually incorrect. It should be "10 Items or Fewer."
Why? Because "items" are quantifiable, you can count out 10 items. Use "fewer" for things that are quantifiable, like "fewer M&Ms" or "fewer road trips." Use "less" for things that aren't quantifiable, like "less candy" and "less traveling."
Principal with principles:
Some grammar mistakes people make is when they end up confusing ‘Principal’, who factually is a person presiding over an institution with ‘principle’ that literally means rules or fundamentals to guide your acts.