I pretty much only write information articles right now, so I don't have to bother with past/present tense. But as far as I'm aware, use past tense when you're writing about something that happened earlier (they went to the house, they did this..) and present tense when writing about something as it is happening (they are going to the house to do this..) You can decide what tense your story is in, just try not to change it around mid-story.