Stop drinking soda, fruit juice, beer, or anything that contains sugar or high-fructose corn syrup and drink water instead. Lots of water.
Stop eating white bread, bagels, cake, cookies, muffins or anything made with refined flour and/or hydrogenated oils. This is probably 80% of what is available in a regular supermarket.
Watch your intake of starchy foods like potatoes and corn. They break down in your system quickly and get stored as fat if you are taking in more than you can consume.
Eat lean meats (chicken, turkey, fish) that you grill, broil or bake. If you must fry, use olive oil, not butter or lard.
Practice portion control... as mentioned in another thread, restaurants give you way too much food. Take half of it home with you, and try to eat at home more.
My trainer suggested a 40 carb/40 protein/20 fat ratio (by grams). You can use dailyburn.com to track how much you eat. It is a great site, and there are others out there like it.
If you are also trying to add muscle mass you need more protein than fat. You probably do not want all of it to be meat. Look at lower fat, lower-cholesterol dairy options like cottage cheese and Greek yogurt to make up the difference.
Watch your salt intake as it can be surprising how much you can take in without adding any to your food. Dailyburn helps with this too.
Eat slower, less, more often, and pay attention to how you feel. Try not to wait til you physically feel hungry to eat, and try to stop eating before you feel stuffed.