Practice noticing where you hold tension in your body. For example, do you hike up your shoulders, brace in your belly, or clench your jaw or buttocks?
Wherever your tense places are, momentarily contract the muscles of this area more strongly, then rapidly release your muscular effort. In addition to the body areas you choose, also include this process for your hands, feet and all facial muscles.
Contract and release each area at least three times, imagining you are turning up the tension on a dial. Keep your breath flowing, despite the effort. After the dial is at the highest setting, then imagine hitting a red release/reset button in the middle of the dial.
This process will help your nervous system relearn how to let go of un necessary muscle effort in your problem tension zones.