* Time: The most basic guideline is the time of the action or state. Past actions are usually in the past tense, present actions in the present tense, and future actions in the future tense.
* Context: The context of the sentence can help determine the tense. For example, if you're talking about a habitual action, you might use the present tense even if the action is happening in the past or future.
* Sequence of events: The sequence of events within a sentence or paragraph can influence the tense used. For example, if one action happened before another, you might use the past perfect tense for the earlier action.
* Relationship to other verbs: The relationship to other verbs in the sentence can also influence the tense. For example, if one verb is in the past tense, another verb that describes an action happening at the same time will often be in the past tense as well.
Here are some things that are not guidelines for verb tense:
* The length of the sentence: The length of the sentence has no bearing on verb tense.
* The subject of the sentence: The subject of the sentence might influence the verb's form (e.g., singular vs. plural), but not its tense.
* The mood of the sentence: The mood of the sentence (indicative, imperative, subjunctive) can influence the form of the verb, but not necessarily its tense.
Let me know if you have a specific example in mind, and I can help you determine the correct tense!