You have to establish the ground rules to your story right away

This show really did not have any twists. It just had the writers changing the ground rules of the story and thinking those were twists.
When the show started I thought I was watching a realistic dramatic mystery. Then, a couple of hours into the story a supernatural element is added to the mix. Wait...WHAT??? I thought this was a REALISTIC drama? That's what it seemed like at first. But now we have people using mystical powers to do things. Then, much later in the series, we find out that not only can people do this really cool supernatural thing, but they can also do this EXTRA thing as well. ("Yeah but, why didn't you tell me that at the beginning of the story?" "Because we didn't want to give away our TWIST ending!" "Well, no, that's really NOT a twist ending......"
Again, establish your ground rules at the beginning. Don't keep changing the rules in the middle (or towards the end) of the game!