Questions about diet

My father's battle with heart disease has opened my eyes and made me look at my lifestyle and eating habits. The question is where do I start? What is the recommended maximum amount of your daily fat, cholesterol and sodium intake? Out of all three of these which one is most important? My mom seems to be concentrating a lot on the sodium intake and I was wandering if you all knew what the effects were of sodium on the heart. Thank you so much for any help! Jennifer