Along with narrative voice, another aspect to consider early on is the tense you want to write your story in. Writing the narrative in past tense with the character dialogue in present tense has been the most popular method for a long time. This is also the most comfortable and familiar to readers. But, increasingly, writers have been experimenting with tense, especially in shorter works and literary fiction.

Selecting the tense for your story

The tense you use can add an extra element to your writing style. Past tense is a comfortable friend, and where present tense can sometimes stick out like scaffolding, past tense disappears into the background, much like the "said" dialogue tags.

Present tense has a faster pace than past tense. Combined with a first person narrative, a story written in present tense puts the reader directly into the action with the sense of immediacy and urgency that you create.

Pluperfect tense (past perfect tense)

Mike had met Joe previously.

Lengthy flashbacks don't need to remain in pluperfect tense when you're writing your narrative in past tense. This is especially relevant if dialogue is quoted in the flashback scene, as it's jarring for the reader to see "had said" too often. The opening sentence or two indicate the reference to the past; once this is established the narrator can move into that "past" scene, making the action current, as long as the start and end points are clear to avoid confusion.

Mike sat at the café, thinking about the first time he had met his wife. She had worn a white dress. He walked up to her, feeling nervous, and asked for a dance.
Her boyfriend interrupted rudely. "How dare you speak to her," he said.
Mike's thoughts returned abruptly to the present as the waiter asked for his order.

If you find yourself writing "had" often in scenes that are too short to easily move into current action, you might want to consider using present tense instead for your narrative, so that references to the past take the easier past tense.

Mixing past and present tense deliberately

I've read some interesting stories using a mixture of tenses. One book involved a current investigation that triggered constant flashbacks for the protagonist to a previous investigation. The author handled this by separating the two stories and writing the main narrative in present tense, alternating full scenes of present tense and past tense reflecting the present and past respectively. It helped to clarify for which case clues were being processed.

Another story was written in first person past tense in a confessionary style. When the narrator spoke of scenes that were emotionally "present" to him, he slipped into present tense narration. Take care with this technique, as you need to have a good handle on your own grasp of tense.

Inadvertently mixing tenses

Some writers find they unintentionally mix their tenses. There are two main reasons for this. One is not being able to separate dialogue from narrative in your mind. Past tense creeps into the characters' words, and, also, when the quotes close, the narrative continues in present tense for a few words.

The other reason is the tendency to tell someone about a past experience using the present tense: "So, I order the fish, and it arrives, and it's still got the head on, and I absolutely freak." Listen to yourself in conversation next time - do you drift back and forth from past tense to present tense in your speech?

The simplest (shortcut) way to deal with a tense mixing problem is to switch to using present tense for all your stories.

But if you want to train yourself so that you have the choice of which tense you use and when, try some dialogue and action exercises. Write the dialogue in present tense, then immediately follow it with past tense action. You might even want to try monitoring your own speech and "correcting" yourself when you use present tense to describe the past - just to help yourself gain awareness of the differences.

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To help you get a handle on tenses and other grammar issues, you need a good grammar guide. Strunk and White's Elements of Style is the definitive guide - this is the brand new illustrated version to make your grammar checks a little more fun.
Painless Grammar is a grammar guide for school students, but I'm suggesting it for adults who really battle with grammar concepts and need plenty of easy-to-remember examples.