If you are a tight player, if you rarely bluff, then YES you should show your cards when you bluff because it not only gives players a false image of your game, but it also taunts them to "come get revenge!" Both work in our favor, and this is my preferred method of play.
If you are a loose player, you should NEVER EVER show your bluffs, the worst thing we can do is give our opponents a peek into our mindset. How could us showing a bluff possibly work in our favor if we intend to continue to bluff at hands?
So in brief, the answer is, always do the opposite of what you are really doing, that's the best way to keep our opponents guessing.