the biggest challenge with updo's is the loose natural look, but you need to approach this look with the same mindset (and just as much hairspray)that you use for the neat, coiffed looks.
first off, the client should arrive with hair that is dry and ready to be put up- not greasy, but not freshly washed- day old is best.you aren't going to do any blowdrying before you start putting the hair up. i usually hot roller set the clients,using the biggest rollers, and hairspraying each section as i roll. the makeup can be going on one of them while the rollers cool.
the basics apply here, back comb and spray each section as you go along,forming the style you are going for, smoothing lightly,and pinning firmly. the trick to having the hair appear loosely put up is to create the illusion with the front and hairline areas, loosely attatching them after you have made the foundation secure,layer by layer.it just looks loose, it isn't actually loose. it's hard to explain without showing what i mean, but just as you would make the final layers of an updo sleek, you can make them casual and loose- looking.
the one look that wedding girls want alot these days is rolled at the nape from one side to the other, then either unfurls as a messy ponytail, or is knotted behind the ear.easy!set, tease, place, pin, spray!i find hot rollers are faster than curling each tendril with an iron, but i do touch up at the end with one if needed.
as far as the timing goes, prep everybody, send some to makeup,set yourself a timer that only you know about,decide how much time you are going to allot to each client, and focus on one at a time. an assistant with pins and spray would be ideal as well.the bride is your main priority, so i would get her done first, and send her off to get ready.then go down the line from there-maid of honor, etc.then, hopefully, there will be just blowouts for mothers of the bride and groom!
a good non sticky hairspray is essential, and no matter what the client says, it must be used for any updo that you want to last throughout a wedding day/night. i prefer shaper, but everyone has their fave.
good luck to you!!