I was wondering where you went

.
Apostrophe errors - Sentences with apostrophes may sound natural when reading out loud but the position of the apostrophe could be the problem. Is the subject singular or plural?
The student's assigment involved politics. (Singular - one particular student had an assignment that involved politics.)
The students' assignment involved politics. (Plural - many students were assigned a project involving politics.)
Both sound the same when spoken out loud, but the position of the apostrophe changes the nuance of the sentence.
Then there are those other words such as children/child that are tricky.
The child's room. (One kid has one room)
The children's room. (The room is shared by two or more kids)
Same is true of man/men, woman/women.
Also could be a slight error where no apostrophe was placed but should have been:
The families house was old and rickety. (Sounds correct when read aloud but should be: The family's house was old and rickety.)
Since apostrophes are one of the issues, one proofreading tip would be to use your word processor's FInd command and search for all instances of an apostrophe ( ' ) as well as "ies." Maybe even search for 's and s' (I omitted the quotes so that you can see the characters easier) Then look close and hard at each instance of words that may have an incorrect apostrophe.
Grammar's tougher to guess about without seeing the sentences in question. So many possible issues such as subject verb agreement, run on sentences, etc. Maybe post a brief excerpt? Pick one that you think might be troublesome and we'll see what we can come up with.