Everyone knows time is vital, and most people never have enough of it. Thus, it shouldn't be a big surprise that time is important when writing too.
Most, if not all, novels are written in past tense. I did something, talked to these people, and this and that happened. Or, in third person, he and she did something, and they met a guy with a machete. Present tense is happening right now. I, for example, sit here writing on my blog.
This sounds easy enough, right? Well, when I started writing, I mixed past and present all the time and wasn't even aware of doing it. I submitted a draft of one of my books, and in the letter I got back, the acquisitions editor said the story showed promise and had an original story line, but my constant switches between past and present tense were off-putting. I said, "My what and my what?" To remedy the problem, I started using the word "had" for everything, just to make sure I stayed in past tense.
Anyway, I'm not the only one falling into this pothole. I've been trying to read a book for months now. It has a science fiction storyline that's right up my alley, it has wonderful characters, and I am eager to see what happens. Every time I start reading I only get a few pages, because the author switches between past and present tense in the middle of sentences, and my brain wants to tie a know on itself trying to figure out what's really going on.
Moral of the story? Just like when we talked about first and third person a few days ago, pick on and stick to it.
If you're writing about a book or movie, you always write in present time.
For example, let's say a book says, "Bonnie took the bus to work, and a rugged man sat down next to her. She tried to shrink into the corner to get away from the musky scent of sweat and whiskey that surrounded him, and didn't even notice he picked her pocket."
If you want to recap this correctly in a review, synopsis, or whatever you might be writing, you do it in present time. "When Bonnie takes the bus to work, a rugged man picks her pocket."
When writing the actual story, most people choose past tense, and accidentally slip into present.
Examples of what not to do: "When I sat on the bus home, I know there will be a package waiting for me." Or, "Her eyes wandered over his hair, it's glittering like gold in the sun."
It should be: "When I sat on the bus home, I knew there would be a package waiting for me." And, "Her eyes wandered over his hair, it glittered like gold in the sun"
It's not difficult, and doing it right makes the material much easier and more appealing to read.
Good luck! :-)