At the salad bar, all of the items for your salad are laid out for you to choose what you would like.  Buffets usually have quite a large selection for your meal with the food in large pans that are kept warm or cold depending on the dish.  A pot luck dinner is usually a more informal meal with everyone bringing a dish to share.  In each case, there is food out for you to serve yourself.   

You will usually pick up your plate where the food is laid out.

Patiently wait your turn and avoid cutting in line.

Use the utensils provided to put the food on your plate.  Do not use your hands.

If one food accidentally drops into another, use the utensils to put it back.

Only take as much food as you are going to eat. 

Do not eat while in line.  Wait until you are back at your table.

If you feel you may sneeze or cough while in line, excuse yourself from the line so that you do not sneeze or cough in the food.

If it is a pot luck dinner, make sure everyone has been through the line before you go back for seconds.