How do I reduce the risk of a heart attack via coronary artery blockage?

Proactive care. Big topic. Briefly: maintain healthy weight, exercise regularly, eat healthy diet, don't use tobacco, limit alcohol consumption, manage stress, have regular physicals with a physician focused on proactive care. Eval generally looks for high blood pressure, diabetes/pre-diabetes/insulin resistance, cholesterol panel. More advanced "cholesterol" testing is available and better at predicting risk.
Healthy lifestyle. Control body weight, high blood pressure, diabetes, don't smoke, live healthy and if you have known coronary artery blockage, talk to your cardiologist about whether that can be opened up by a procedure or you need to take blood thinners. An Aspirin a day is a must!