Stress is well known to lead to high blood pressure. There are many stress busting techniques that you can learn but one of the best for lowering the blood pressure consistently is meditation. A few minutes of deeply relaxing meditation morning and evening can have a big effect on your stress levels throughout the day.
You can learn meditation with a local class or on your own from a CD. Most Buddhist groups teach meditation but it is not only a Buddhist practice. Many yoga teachers include meditation in their classes or you may find relaxation classes which will be based around meditation.