One of the easiest ways to set a table for a formal dinner is to start by setting the table as if you were eating with family - the basic setting that we all learn in school: plate, cup, napkin under the fork on the left, and the spoon and knife on the right. Add other silverware and plates as needed. For example, a salad fork if salad is going to be served, and a soup spoon if you’re doing soup. If you’re serving dessert but don’t want to tip off your guests, you can bring the dessert forks out when you bring the dessert out.
For a more formal feel, set out placards to do a kind of arranged seating (also good to keep troublemakers apart).