One of the panels at the RT Booklovers convention hosted Patricia Briggs (amazing author of the Mercy Thompson series) and several other amazing women to talk about how to increase tension in your writing. Many things were said, but what I took away from this talk was that only you (as the creator of your characters) will know how to create tension in your own work.
Here are the questions you should be asking yourself (because only you can answer them). The answers will help you create tension in your writing:
1) What stands between your character and their goal?
2) What happens when two characters want the same thing or the opposite thing?
3) Is your character trying to reject their nature or embrace it?
3a) What are the repercussions of rejecting/embracing their true nature?
4) What happened in the past to create their present goal(s)?
5) What are your character's disadvantages in trying to reach their goal?
6) What lie does your character believe about himself/herself?
7) In what way is your character broken or flawed?
8) In what areas are your character(s) struggling to grow?
9) Put different characters together and see what happens.
a.) How do their personalities clash?
b.) How do their ambitions (or lack thereof) create tension?
c.) If they must work together, what are all the pitfalls of that partnership?
d.) If they oppose each other, in what ways do they sabotage the other's schemes?
Hope this helps! :)