There may be many reasons why you want to reduce stress - and knowing what is causing your stress will help in any stress reduction strategy.
However, when stressed there is tension in the body, and most stress management techniques involve relieving this tension through relaxation exercises. These relaxation exercises include mind to muscle techniques, such as meditation and relaxing imagery. Alternatively, they can include muscle to mind techniques, such as progressive muscle relaxation, exercise, or breathing.
I generally find that breathing exercises are the way to go for a quick way to counter the stress response.
When stressed you are more likely to breath rapidly and shallowly. Does this sound like you? If so, then taking a few deep breaths from the belly will counter this stress response and get more oxygen to your body and muscles. Also, if you focus on simply taking a deep breath, you will find that you are less likely to focus on thing that is causing you immediate stress.
If you would like to know more about different breathing exercises then check out this page:
All the best