Verbal cues are short, sharp, clear words that name a behaviour. What is important, is that the behaviour should be named in one word and only that word. Everybody training the dog should use the same cue. Do not make complex commands, e.g. “sit and stay in one place”. That is just too much to digest.
Do not be ambiguous if “down” means lay down on the floor, do not use the same command to say “jump off the sofa” or “look under the table”. Name the behaviour only when your dog performs a command 8 times out of 10 correctly. Naming the behaviour and using verbal cues too early will only confuse your dog.