I like to think of tension in layers.
Layer 1: The obvious and immediate need for food, fire, shelter or whatever external struggle your characters are in. Maybe it’s not survival, maybe they mistakenly ended up in a mountain cabin together. Fine, but Layer 1 is all about that external push and pull.
Layer 2: You have two people. Which one is your main character? Layer 2 deals with that character’s internal fear, determination and/or desire within the scene. In Summer by Summer, my heroine is the main character.
Layer 3: This layer deals with my hero. His fear, determination, and/or desire within the scene. Remember, these are specific to the scene. Of course, your two characters need an overall character arc, but we are breaking this down scene by scene. This will likely tie into their overall internal goal and internal conflict, but it will be unique in each and every scene.
Layer 4: This is my favorite. The CLASH between these two characters. Think of your favorite books. I bet one comes to mind where there is a real and intense clash between the two main characters. Never underestimate the power of the clash!
Now we put it all together. You’ve got powerful scenes people will be compelled to read and read and read. Can you put all four layers in every scene? You should try to. That should be the ultimate goal. Everything you write will be richer, more vivid, more powerful if you apply these layers. Good luck and happy writing