Rules 11 and 12

11. Unnecessary Shift in Pronoun

We went to the baseball seminar at the high school, and I learned how to throw a curveball.


We went to the baseball seminar at the high school, and we learned how to throw a curveball.


When you use a pronoun, you need to make sure to keep the same pronoun though out the sentence.

12. Sentence Fragments

(Missing Subject) Went to the store to buy some groceries.


My mother went to the store to buy some groceries.


When you write a sentence, you need to make sure that it has a subject and a predicate.