Icelandic table manners are a lot like American or European table manners. Keep your elbows off the table, but it’s okay to rest your wrists on the table’s edge. Use your left hand for your fork and your right for your knife.
Don’t take more food than you can realistically consume if you’re eating at a communal table. It’s bad manners to throw away food in Iceland. Instead, just take a smaller portion and ask for more if you want to sample extra entrees.