Most weddings do not need a rehearsal depending on how large it is. All rental halls have a staff person who schedules and conducts a walk through. That is the person to contact and talk over when and how the rehearsal is to be conducted. When a couple contacts a person to participate they need to discuss with them what is expected. Think about how many attendants and realize the more you have the more rehearsal it takes. Small weddings a walk though can be done right before the ceremony. There are many web pages with info on who walks when and who sits where. Reading over those before the selection of attendants help you plan before you ask people to be attendants. Wedding planners are well versed on what is needed for big weddings and may be needed to help you plan. Small weddings a friend who has done weddings may be helpful to discuss things with.
Advance preparation by reading up on rehearsals, processional, and recessional is best before asking someone to be an attendant. Usually best man, and maid of honor is all that is necessary with ushers to seat people. Plan out in your mind who stands with whom. Who seats who, when, where. What children will participate and realize kids may wander off. keeping things simple is best. All wedding halls have a system they follow for each wedding and they use that program for the rehearsal. More or less a package system they follow for each wedding.
More details can be found by doing a search on the web like this planning page at Martha Stewart: http://www.marthastewartweddings.com/ .
With a chart for standing: http://www.marthastewartweddings.com/230635/wedding-ceremony-basics/@center/272440/wedding-etiquette-adviser#143199
Realize it is your wedding and follow a plan you like best.
Here is a nice web page with outlines on wedding planning. Online Marriage Preparation