Structure first
Entrée is a starter, plat the main, and 'formule' or 'menu' means a fixed-price set. Knowing the layout gets you most of the way before any vocabulary.
Cooking words carry the detail
Grillé, rôti, à la vapeur, en croûte and fumé describe method. These endings repeat constantly, so a small list unlocks whole menus.
Deduce, don't panic
Use cognates, the price and the section heading. A cheap item under 'entrées' with 'fromage' in it is unlikely to surprise you.