Choose not to waste your precious present life on guilt about the past or concern for the future. Learn a variety of relaxation techniques and practice at least one regularly. When we accept others, ourselves, and situations for what they are, we become more effective in influencing them to change in the way that we'd like them to. Feel the difference in your mental attitude and your body when you do this. Become more aware of the demands you place on yourself, your environment, and on others to be different from how they are at any moment.
Demands are tremendous sources of stress.
If your schedule is busy, prioritize your activities and do the most important ones first. When you read your mail, act on it immediately, don't put it off. Take frequent relaxation breaks. Organize your life to include time for fun, spontaneity, and open spaces. Set a realistic schedule allowing some transition time between activities.