I pay most attention to the calorie, fat, salt and sugar contents, in that order.
If you want to lose weight, as most seem to, cutting calories is the only way to go. Simply eat fewer calories than the minimum you need to maintain your weight and the pounds WILL come off. Foods lower in sugar are almost always lower in calories and fats.
In my family my wife needs to avoid high salt-content foods because of high blood pressure, and I avoid excessively sugary foods to guard against diabetes and dental problems.
Nothing is 100 percent, but the nutrition labels can give you a good idea of what you're putting into your body.