However, understanding verb tense can make maintaining consistency a bit easier.
So let's break down some of the more common ones used in writing. For the sake of simplicity, I'll stick with simple tenses.
Present tense verbs generally describe the here and now. They are frequently used with many nonfiction topics when the writer is discussing his/her own ideas or factual material. While it's not as common in fiction, the use of present tense is becoming more accepted, as many authors opt for it in an effort to create a sense of urgency. Although many readers (and writers) tend to prefer past tense here, present tense can be powerful if handled effectively. The following is a present tense example:
Myrah glances over her shoulder to find her pursuers still close behind.
Past tense verbs are used to discuss events that already occurred. It is still the most commonly used in narrative fiction as well as historical and biographical topics. Readers (and writers) prefer past tense because of the sense of completeness it offers. It also invokes a sense of a story being told orally (like a friend having lunch with you and relaying an experience from his weekend).
Sheila lifted the rusted chain from the box on the floor.
Future tense is used to discuss the events that have not yet occurred. This includes plans and topics that involve predictions (economics, meteorology, etc.).
The band will return to the studio to resume recording in May.
Controlling Verb Tense Shifts
Since verb tense establishes time, a shift alerts readers to the temporal relationship between events (that something happened before or after something else). This is why consistency is important within a narrative. You should not shift verb tenses unless the narrative requires it. Consider the following example:
As I approached the building, I notice the security guard was missing from his station.
As you can see, an unnecessary shift can be subtle. The sentence should read like this:
As I approached the building, I noticed the security guard was missing from his station.
However, if the events in the narrative call for it, by all means change tenses:
Adam reaches in his pocket and pulls out the old coin he found in the attic.
Ultimately, the events dictate verb tense. Be sure to shift cautiously and be mindful of it during the revision stages of your writing.