When asking for something one important phrase you need is “Chtěl/Chtěla bych…”. The sentence is the equivalent of “I would like…”. Stick what you want on the end of the phrase, e.g “Chtěl bych prosím jídelní lístek,” (I would like a menu please.) When ordering food, it is more appropriate to use “Dám si…”, or if you want to be extra polite, say “Dal/Dala bych si…”.