When you are standing on the podium and you tell an ensemble, through your nonverbal communication, about the tempo, the character, the style and how they should enter the ensemble looks to you for a preparatory gesture. This is the motion that immediately preps the ensemble to give them all they need to play on.
First try this in front of a mirror at a moderate tempo. Do the preparatory beat and downbeat and then stop. Take a breath and reset. The breath is helpful. If you cannot get a feel for what is happening you may need to simplify your gesture, you should be able to anticipate your downbeat from your preparatory gesture. Make sure the ictus of your downbeat is clear. Are you accidentally rushing your downbeat? The last gesture should belong to the pulse of the music that is to follow.
Now, add the breath again, but this time quietly synchronize the breath with the gestural preparation. Do not overuse or exaggerate the breath. It should be used to help the downbeat, not just for effect. Now practice again with a metronome and make sure that your gestural invitation to the ensemble breathes within the metronome marks. Make sure you land the first downbeat ictus with the metronome and that your preparation is clear for all to see. Is there room for an ensemble member to prepare? Is your preparatory gesture large enough? Would a wind player know when to breath and get ready to play?
Finally, think of the character and tempo of the ensemble entrance. The preparatory gesture shouldn’t be some extra thing that you do. If you want to enter on the first beat (a.k.a. the downbeat) in a four beat meter, you would use the gesture traveling through the fourth beat to prepare the ensemble to enter. If your preparatory gesture is large, but the downbeat is small are they saying two different things? They should match in size, speed, and direction. A common problem for beginners is to focus only on the downbeat and neglect a clear preparatory beat, or make the downbeat larger thinking a clear downbeat equals a clean entrance. The gesture should also invite the ensemble to enter with a tempo and not be too big and vague for the ensemble. Make sure the gesture is clean and clear and that all the information the ensemble needs is being provided. You could also try this exercise with entrances on different beats and not just on the downbeat. It would be good to know how to prepare a pickup to a downbeat and also a gesture to get an ensemble to enter on any beat within the measure.