In the military, orders given by a senior to a junior member are typically given in two parts: the preparatory command which is intended to ready you for action; and the command of execution which tells you when to take action.
A simple example is when a drill instructor wants a group of recruits to move from one place to another: "Forward, march!" In this case, forward is the the preparatory command, and march is the command of execution. When these words are spoken, or perhaps yelled, the recruits know where they are supposed to go and when they are supposed to move.
Another example is "Double-time, march!" Double-time refers to a specific marching cadence, and march, of course, tells you when to move.
Things get more complicated with combined preparatory/execution commands such as "fall in", or "at ease". The key with this command is the tone that the speaker uses which is typically different than the usual preparatory/execution sequence.
Learning to march with a group of recruits was one of the most enjoyable aspects of my naval officer training. Although it took quite a bit of time to get to the point where my class could move as a fully-coordinated element, the results were astounding when we became proficient at it. The key is practicing and training regularly in order to learn to anticipate the shift in tone and timing of the action so that the commands become second-nature.
When people know where they are supposed to go and when they are supposed to move, it is easy to get people from one place to another or to accomplish a specific task. When leaders skip the preparatory command and go to straight to the command of execution, confusion can ensue if it isn't entirely clear what people are supposed to do.
As a leader, think carefully about what you do to prepare people for action. What do you do to get their attention? Clear your throat? If you are a conductor, you might tap the sheet music stand with your baton. Or you may rise from a seated position in a meeting.
The signals we give to people can have a major impact on how people react to us. Consideration of how thoughts are transferred from one person to another, especially if an action is required, can impact your success.