When should you assign a word to the command and start saying it out loud? How should you start adding verbal cues?
Before naming the command, teach your dog to perform it reliably. When practising the command by luring or hand signals, the dog performs correctly 80% of the time, e.g. rollover, only then name the command.
If you keep repeating the verbal cue “rollover” before your dog knows how to do it, the verbal signal will not help the dog, because it does not understand the meaning of the word.
Attaching a name to the command too early is an additional distraction. Also, your dog will associate the word with a half-finished version of the behaviour, this can result in half sit or a dog who thinks down is like the yoga position.
Repeat the behaviour until it happens easily at least 80% of the time. Add the verbal cue just before the dog does the behaviour to associate the word with the appropriate response.