This is needed because if there is no tension there is nothing for the reader to keep the reader guessing. You want to keep tension in different ways, plot wise, internal struggle of the characters, the relationships between characters, and the antagonists own impact on the main character.
My most recent example of creating tension is internally. My character is struggling with ways to reveal her secret to her family, because she isn't sure how they will accept her. Now I have set up the parents as loving people, yet her secret is so world changing that it might even change the way her parents view her.
Now this works on the internal level, but I've also added some external plot points that take this tension even further, which I won't get into here as it's still a Work in Progress.
So my question to you is, what is your most recent example of creating tension in your writing? Are any of you working on a horror book that has a lot of tension for scares? Romance books where the characters are separated by their own devices? Let me know, but don't let the tension get to me...