1) When you are deciding what you want to order, by law the restaurant has to provide how many calories are in it. That can really help you narrow down what you want to eat. Just pick the ones with the lowest calories! That works most of the time...
2) Another tip is when you are looking at the menu, it really helps to get the healthiest choice, such as salad, over a deluxe double cheeseburger. I know it seems like common sense, but people tend to side with their taste-buds over their gut feeling.
3) Finally, your drink. It appears to be a small component to your meal, but it can play a huge part in calories. The only things in soda are artificial flavors, and empty calories. Empty calories are calories that don't give you energy, they give you body fat. So if you get anything at all out of this tip, it's to skip the soda.
All in all, fast food should not be eaten often. I'd recommend once a month. But if you truly have nowhere else to eat, these tips will help you survive ;)