Pose a critical mystery early on but delay the answer for as long as possible.
In music, tension is the perceived need for a "drop" or harmonic resolution. tension
To create "tension" as a central feature in your work, you need to deliberately establish an imbalance that demands resolution. Depending on your medium—writing, music, or design—the methods for building this "strain" vary: Pose a critical mystery early on but delay
Pit two fully-formed characters against each other, where one can only win if the other loses. tension
Impose a strict deadline to force characters into desperate choices.