If you're a writer or you're simply communicating with someone on a formal basis, it's important that you avoid at all costs the most common yet critical grammar mistakes. Bad grammar can be distracting and makes your writing appear sloppy.
Spelling and Grammar Mistakes How to Avoid Them
Misusing the Apostrophe
Apostrophes are used in two scenarios: to show possession or to create a contraction. Don't get them mixed up. It really is unforgivable.
– It's such a nice day today (contraction)
– The cat scratched its owner (possession)
Your and You're
Again, it's possession versus contraction.
– You're going to regret eating your cake.
There, Their and They're
Don't ever get this one wrong either. Not only will you look unprofessional but it will take the reader some time trying to figure out what you mean.
– They're eating their ice cream over there.
When you see a piece of writing with too many commas you end up having to read it over and over again to try to decipher the original meaning. Commas aren't simply used when there's a pause in speaking. See Rules for Using Commas.
If too many of your words are randomly capitalized your writing starts to look sloppy.
Capitalize names of people, places, books, movies, languages, brand names, titles, days, months, holidays, the first word in a sentence and the pronoun I. More rules here.