Take a moment to observe your breathing
Don't change or control it. Just pay attention to the movement of the air in and out of your lungs.
When you're ready...breathe out completely emptying all the air from you lungs.
Next, allow you body to take in all the air it wants (through your nose).
Feel you abdomen expand enabling you to draw the air deep into your lower lungs.
Exhale quietly and completely through your nose.
Continue abdominal breathing for as much time as you have.
Allow relaxation to occur at its own pace.
How long is best?
A minute or two cam be helpful, ten minutes or more offers deeper relaxation.