Make a budget - one that is realistic and allows for a specific amount of dosh to be set aside for food. Knowing how to cook helps, as there is less chance that you will ruin good food, or over estimate ingredients etc. Knowing the amount of inveterate packet openers in the youth of today however, just the basics is often a good place to start. Knowing the basics of nutrition is also a winner in determining who will survive, and who will either put on loads of weight, or waft anorexically from tutorial to tutorial. Its not always how much you eat, but what it is you are eating that is important.
Health is a valuable commodity, so lets first look at where the money goes.
A word from the wise, if you smoke cigarettes, Stop. They are unfeasibly expensive, give you filthy breath, don't really suppress your appetite and if that isn't enough, they will kill you. Now that soapbox is over, my point is about sensible marketing. Tip number one is to shop weekly, not daily if possible, as this tends to minimise impulse buying and allows planing of meals to go ahead. If you live in Sydney, utilise the benefits of paddy's markets on a Saturday or Sunday.