As a writer, you want your reader’s experience to be as smooth as possible. That ease is why you don’t want sentences like this one:
I am eating lunch when you called me.
If you feel confused by that sentence, you’re right. The first verb is in the present tense, and the second verb is in the past tense, but switching between tenses isn’t usually allowed. We can improve the sentence by writing:
I was eating lunch when you called me.
I am eating lunch when you call me.
If the actions in your sentence take place at different times, then you have to change the tense by using a subordinate clause.
Example: Since it will be dark in half an hour, we are going for a walk now.
Example: The builders are working hard after the tornado hit last week.
You need to be consistent about tense in your paragraphs and copy as well.
You can choose to write in the past, present, or future, but you need to stick with whatever you choose. Tense consistency is key for readability.