After misuse of an apostrophe / plurals and getting the various forms of they’re / their / there confused the NUMBER ONE grammatical mistake I see virtually every day is the misspelling of you’re – as in you are. An example of a sentence would be: I can see you’re really good at English grammar and not I can see your really good at English grammar.
For the millionth time, you’re is a contraction of the words you and are, meaning you are.
The word your is the possessive, as in your mistake, your lack of basic English grammar.
What I get so often are emails saying your welcome meaning you are welcome / no problem.
Your welcome means the welcome you receive e.g. when you arrive at a party or whatever.