Some of the most common grammar mistakes are as follows.

1. Subject-verb Agreement Errors
2. Sentence Fragments
3. Misuse of Contractions and Apostrophes
4. Passive Voice
5. Dangling Modifiers
6. Comma Splice
7. Run-on Sentences
8. Ending a Sentence in a Preposition
9. Wordiness
10. Wordiness
11. Incomplete Comparison or Expression of Degree
12. Mixed Construction
13. Pronoun Disagreement
14. No Clear Antecedent
15. Mixing Up Spellings
16. Mixing Up Possessive and Plurals
17. Mistakes with Well and Good
18. Mixing Up Adverbs and Adjectives
19. Confusion Between Fewer and Less
20. Title Capitalization Problem
21. Your/You’re
22. There/Their/They’re