Practice body awareness. Here are 5 things to check:

1. Are you clenching your jaw or holding the muscles in your jaw tightly? Open your mouth as wide as you can for a few seconds then let it go, relax your jaw. How does it feel different?
2. Are you squinting or scrunching up the muscles around your eyes as if you were worried? Squeeze your eyes tightly and furrow your brow for a few seconds then let it go. Do you feel your whole face relax?
3. What about your shoulders? Are you holding them up even a little bit? Or do you feel like a turtle going into its shell with your shoulders up around your ears? Raise your shoulders up as high as you can for a few seconds then let them go. Take a deep breath. Doesn’t that feel better? 
4. I bet you never thought about your tongue being connected to all this tension. Relax your tongue, bringing it down into the floor of your mouth. What does that do to your jaw and to your neck and shoulders?
5. Are you barely breathing when you are focused on a task or tense about something? Try breathing deeply several times, filling your lungs and suspending your breath in that state for several seconds, then blowing out to empty your lungs completely until you naturally have to take a breath again. That place of stillness at the top and bottom is an amazing sensation, and very stress-reducing in its effect.