First, consider nutrition. Try to avoid processed foods high in calories and additives. While quick to prepare, these foods have ingredient lists you can't pronounce and are typically high in fat, sodium and added chemicals. Whole foods have fewer than five pronounceable ingredients and are fresh. Shop for grains in bulk and store them in airtight containers for quick access and to preserve freshness.
Next, consider your budget. Many people eat fast food because it's cheap. Like packaged, processed food, it isn't real food and will do long-term damage to your health, making it more costly in the end. Buy in bulk, but don't overbuy produce or you may end up throwing much of it away when it spoils. Shop locally when possible. Buying directly from the farmer is generally cheaper, and the food is often healthier than in the supermarket.
Plan your meals carefully and do all of the shopping at once for the week. You can also save time by cooking a couple of meals for the week over the weekend, making enough to have leftovers for lunch or the next evening's meal. There are many cooking blogs and recipe databases online for inspiration and time-saving tips. They offer many recipes that you can prepare in 30 minutes or less.
For more time consuming dishes, consider making enough extra to freeze a portion, providing a quick meal for busy times. Roast a whole chicken rather than just cooking breasts and use the leftover meat for several easy weeknight meals.