well congratulations I hope it works out for you you can see my projects at
www.akextremelimo.com we generally do a really basic detail every time the cars go out but thats not the norm for the industry. Genrally the drivers are expected to maintian thier cars wich usually consists of cleaning glassware wiping down the interior, pledging the upholstery and a quick vacuum of the floor mats keep in mind its generally pretty dark in limos and so this will keep them running for quite a while now your job on the other hand will not be quite so easy here are my suggestions:
1) make sure you have lighting that you can use inside the vehicle so you can see what your doing.
2) have plenty of towels or applicators many of these rigs have pleated leather and it seems like everyone who rides in a limo wants to wear glitter wich sticks to your applicator and then redeposits itself.
3) rinse out the ice wells real good (possibly w/bleach water) as wine tends to sit in the drains and smells.
4) wear shoes that slip off and on easily our limos have black carpets and foot prints in a perfect limo stand out like a sore thumb.
5) be carefull to give yourself enough time as you don't want to say it will be done at a certian time and either make them late for a booking or give it back to them less than perfect.
well good luck and keep in mind no disrespect to the other comment but its not likely they want the limos cleaned up from the night before but most likely they want a thorough detail that their drivers can then maintain.