This issue shows up in manuscripts that I see and not just a couple of them. Now, I can understand coma troubles—there’s a stylistic issue in play, so you can go for the less or more styles. Commas can be tricky and badly used can lead to awkward sentences. However, verbs tell the reader when something is happening. Get the verbs tense wrong and you’ve got a confused reader who has to stop reading the story to figure out what’s going on.
The worst of this shows up with past perfect tense.
If you’re writing in past tense and you need to talk about something in the more distant past, you need to use the past perfect tense to avoid confusion.
An example of this is you have two characters talking. Let’s say Sue and Larry are having dinner in a restaurant. Sue thinks back to how she bought a gallon of milk yesterday. Maybe you write:
She bought a gallon of milk.
This sounds as if Sue is currently buying the gallon of milk in the middle of a conversation in the restaurant. And the reader goes, “Hun?” The reader now has to stop, reread, and has been thrown out of the story. Do this enough and the reader puts down the book.
The past perfect tense helps the reader figure out the time sequence. She bought a gallon of milk. becomes:
Yesterday, she’d bought a gallon of milk.
Or if you want to avoid “had”:
She remembered buying a gallon of milk yesterday.
Had is not a bad word. Neither is “that” but there also seems to be a trend toward removing both words, and this can make for awkward sentences.
Reading aloud will help you catch these things. So will a copy of Strunk & White’s Elements of Style, a handy small book that every writer needs close at hand.