Eating habits tend to vary dramatically from country to country. In the United States, there really aren’t general rules for finishing your food – unless you had parents who wouldn’t let you leave the table without finishing your plate.
In Spain for instance, you are expected to finish your food…all of it. Not finishing your plate is considered rude to your host or chef. In order to avoid this faux pas, finish your food and do not order more food than you think you can finish.