Knowing when to set your piece is a very important aspect of writing. Are you setting the piece in the past? If so, be careful to maintain the illusion and not include things that weren't invented yet. Having Blargg the Caveman whip out a ballpoint pen is completely absurd, as would be having William Shakespeare use a computer. Sure, these are extreme examples, but even something as innocuous as a tea bag could be just as incongruous in the period of the story. Research the historical context of the period you're writing about to avoid jarring inconsistencies.