Learning Grammar is a progressive activity that is best done over time and with attentiveness to what you read and what you hear. According to Douglas Cazort, author of Under the Grammar Hammer,* the 25 most common grammar mistakes are:

1. Wrong verb tense or verb form
2. Fused or run-on sentences
3. Sentence fragments
4. Lack of agreement between subjects and verbs
5. Wrong word usage
6. Missing comma(s) with a nonrestrictive element
7. Unnecessary shift in tense
8. Missing commas in a series
9. Missing or misplaced apostrophe
10. Unnecessary comma with a restrictive element
11. Confusion of its and it's
12. Dangling or misplaced modifiers
13. Lack of agreement between pronoun and its antecedent
14. Wrong or missing preposition
15. Vague pronoun reference
16. Unnecessary shift in person
17. Comma splice
18. Wrong or missing verb ending
19. Missing comma in a compound sentence
20. Missing comma after an introductory phrase or clause
21. Objective case pronouns used as subjects
22. Double negatives
23. Failure to capitalize proper names
24. Faulty parallellism
25. Subjective-case pronouns used as objects

Once you learn the rules, several attempts of careful proofreading will enable you to catch and to correct these common errors.

*Under the Grammar Hammer was published in 1992 by RGA Publishing Group, Inc.