Advice
 
Some people hire wedding coordinators, but for the others who want to do it themselves or have a family member/friend do the planning, here's my advice.
 
1.  Never just assume the musicians will work it out in the end.  (You can disregard this comment in the hour before the ceremony, at which time you can repeat to yourself "Everything's going to be fine" as you do breathing exercises into a paper bag to keep yourself calm.)  No disrespect is meant to the musicians - the fact is that there are many other factors that affect and are affected by the music, things that no one plans for.  Everything needs to be planned out to the last detail in advance.  If it helps, you may want to create a detailed schedule of when certain things need to be complete, as well as a specific schedule of the ceremony with lighting cues, music cues, staging marks, etc.  While some may view this as being too controlling and anal-retentive, the fact is it helps to get everyone on the same page, and the act of writing it may even help you keep things organized in your brain.  If you need help with constructing the order of the ceremony, the pastor/rabbi/justice or whoever is officiating the ceremony should be able to give you an idea of what they normally do.  Things you should consider to include in this detailed schedule is where individuals are at each point of the ceremony, if they need a microphone, what the PA system settings are for a particular song,  at what point in the processional does each groomsman/bridesmaid enter, etc.    
 
2.  If the number of guests is larger than 30, I would seriously consider making sure there is some way to amplify (to some degree) the bride and groom for the vows.  It's a beautiful thing, but only if everyone can hear them.   If the ceremony is outside, you can expect the sound not to carry as well as inside a room (especially if it's windy or it rains - the sound of rain on a tent can be deafening).  Likewise, you should expect that the sound carries better inside an empty room than in a full one.  This would mean that you can go into a room and check the acoustics, think it's ok, and when all the guests have arrived, people in the back are having difficulty hearing.   A qualified sound person will keep on top of that part, but they need to be able to plan ahead to do that.
 
3.  Make sure that the rehearsal is like a dress rehearsal.  Especially when people are hungry and wanting to get out of there, it's a good idea to have the rehearsal focus on everything as a whole, and have the musicians have a separate rehearsal WITH SOUND SYSTEM (if applicable) earlier in the day.  This way, the final details can be worked out with time for changes to be made, and the official rehearsal can focus on how fast people walk in, where people stand,  or what people say.    The reason I capitalized the sound system part is that depending on the type of song or instrumentation, the acoustics can change quite a bit.  You may say to yourself "well, I know our sound person, and they're great, they don't need much practice."  They may be an amazing sound person, but if they're smart, they'll want to have the extra time to know what to expect and to fine tune the settings.  That's one thing that makes a good sound person a great sound person (apart from sheer talent).
 
4.   Don't forget to enjoy the day - it's not worth it to have a great wedding or party that you didn't enjoy because you were so stressed.  Relax - everything will be fine in the end...if you plan ahead.
 
 
 
 
 
 
 
 
 
 
Unique Ideas
 
1.  Have a processional and/or recessional written for the occasion
2.  If the bride and/or groom is vocally talented, have them sing to one another.
3.  Have a song written for the wedding and have it performed during the ceremony
4.  Have a song or instrumental piece written to serve as a soundtrack for a video or picture slideshow to show at some point during the day (before ceremony, during ceremony, during reception)
5.  If having the occasion professionally videotaped, request a soundtrack be written for it.
6.  In certain circumstances I might recommend putting some or all musicians in the back of the room.  Some pros to that would be:
    A.  The (reasonable) element of surprise
    B.  It keeps people focused on the bridal party and the events of the ceremony.
    C.  The musicians can see what’s going on and be more alert (sometimes it’s
         difficult when all you see are the backsides of the bridal party).
    D.  Sometimes the front can be crowded for space.
The main potential down-side is that if some musicians are up front and others are in the back, and they can’t hear each other, it can be either an awesome experience or a major headache.  So that is why I don’t recommend it for every wedding.  Kids, don’t try this at home.