I also have this problem, I have breathing techniques to use but I find once there is tension there I find it very hard to get rid of! I find my shoulders are raised, by breathing is jittery! Sometimes I find just a few deep breaths help but I find this hard to do in pressures situations I am going to start doing some meditation, relaxation videos, there is loads on YouTube and they just talk you through relaxing, focusing on breathing, I feel like those will help!