WiP Wednesday

I am currently working my way through my action/adventure novel via print out and red pen. I have already made a large change to the beginning and have started to implement a lot more back story that was missing in the first draft to really bring out the main character's motivation and try to get the reader behind him in his life choices more. Another thing that I have been focusing on is really upping the tension, while keeping it relevant to the main plot, which seemed to drag a bit toward the end.

What are some of your tips for upping the tension in a story? I am relying on the character's actions and choices to really center the tension around him and his mission.