Manage your weight; lose if you need to.
Healthy diet and exercise regime; get professional advice (from a doctor, not a gym).
Avoid stimulants such as caffiene, spirits and tobacco.
Reduce animal fat in your diet.
Get enough sleep.
Remove all possible stress-situations from your life. OK, we've all got to work, but anything you CAN eliminate, do so.
Therefore, some relaxation techniques
may be in order.
And there's currently a theory that stroking a cat and listening to it purr lowers your bloodpressure. Of course this only works if you actually like cats, but I do find it calming.