Look at that guy next to you. He's stuffing 6 fries into his mouth at a time. He's chewing with his mouth open! And he's blowing bubbles in his drink! Don't let that be you.

First off, remember that you are eating fast food. This food is meant to be fast and cheap, not good and nutritious. When eating fast food, know that you have already abolished all rules of service and manners. That said, read on.

Remember those manners your parents taught you? Ok good, that's your basic foundation. You might be the only person there who does, but remember those manners before you go to your local McDonald's or any other fast food restaurant.
Go to a fast-food restaurant, order your food, grab it, and sit down.
Use your tray paper for its purpose: to make less work for the guys who wipe them. Stand your side container upright. Even a little grease can penetrate through that paper that you usually don't even look at (look at it after your meal)
Go ahead and fill your cup with a beverage. Grab a cap and straw also, and construct your liquid-holding vessel.

Inspect Your Food;
You will be eating food prepared by people who may or may not find it important to keep your food free of foreign matter. Inspect all food before eating.
Eat your main course:
If your main course is a sandwich, unfold its wrapping. Lay your burger on the wrapping, and encase 70% of the burger in it. Eat your way through, and gradually fold back the wrapping. Beverage should be drunk in moderation with this main course.
If your main course is a salad, lift the lid off, and fit it (if possible) under the container. Apply dressing first, and then croutons (if applicable). Fork through your meal. If there is a side for the salad, eat that in moderation with the salad, along with the drink.
Grab your side -- only one at a time! Dip it in the condiment.
Drink politely -- no slurping or blowing bubbles.
Throw away your trash. If possible, throw all objects on the tray, one-by-one, into the trash can. Keep the napkins for later.

If with someone else, do not bother them if they are breaking any of these rules. Don't start a fight over food. Just set a good example with your good manners!
The maddening rush hour for the store cannot be silenced. You may have to change your rules during the wait for you food.
If you are paying for your meal with cash, and (as an example) your order rings up $3.02, give them the extra 2 cents along with that $5 or $10 bill. It makes the transaction quicker, and easier for the cashier.
This is only good for a meal of a sandwich/burger/salad with french fries/onion rings and a drink.