This is one widely accepted way to place your silverware so that the waiter knows you are finished.

It is polite to wait until everyone is served to start eating, unless everyone has their food except for one or two people and they suggest that everyone begin.

It is polite to wait until everyone is finished eating before leaving the table.

It is not polite to burp at any time, and if you do, it is polite to excuse yourself (＂Excuse me.＂).

Chew with your mouth closed.

Don't talk with food in your mouth.

Don't put your elbows on the table.

When the situation is informal, Americans are generally relaxed about etiquette. If you should make a big mistake, most people probably won't even notice. So relax, and eat up!!