Do this quick and dirty one. Deep breaths in through the nose, out through the mouth. 10 seconds breathe in, 10 seconds hold, 10 seconds breathe out. Repeat 5-10 times. Only concentrate on your breathing/lungs, your heart beat and the counting.

Do that in the morning, afternoon and night, every day when you have a spare few minutes. Enjoy less tension.

I also do it for a shorter period of time when something specifically is triggering me and I need to chill and release some tension from the jaw/neck.