A well-run rehearsal will lower the stress level for everyone! 

thanks to a Wedding REHEARSAL CHECKLIST customized for your wedding, the officiant will Knowing exactly what to do and how to lead a great rehearsal.   here are a few examples from a sample rehearsal checklist:

Before the rehearsal begins:
__ Introduce yourself to the site coordinator.  If you will need a table for “props” on the wedding day, be sure to tell the site coordinator.  
__ Figure out what the spacing should be between the bridesmaids as they process.

If the rehearsal and wedding are taking place outdoors:
__ Take note of any potential noise annoyances (trains, planes, etc.)
__ Assess the bug situation

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Readings
__ Tell the reader to stand in front of the groomsmen at an angle so that he/she is facing towards the guests but is also facing somewhat towards the bride and groom.  For the reading, the groom should shift and face the reader.  (The bride will already be facing towards the reader so she does not have to move.)

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Exchange of Vows
__ If you will be using a handheld microphone, ask the couple if they each want to hold the microphone during the vows OR if they want you to hold the microphone towards each of them when they say their vows OR if they do not want to be amplified.

__Practice the vows with the couple in a repeat after me style.  Don’t rush.  You might find out that you need to break the vows into smaller segments.  Note that in your script book so that all will go well on the wedding day! 

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Exchange of Rings
__Tell the bride and groom that fingers swell on wedding days!  Rings should not be forced on.  If a ring only goes as far as the knuckle, just leave it there.