Congratulations!!!!
If you have never dealt with a crew hanging sheetrock, be sure you have a plan for clean up. Most crews will not clean up their mess.
Be sure that the cut out every outlet and switch box. Count them for every room before they start and then count them when they are done. It's common to have something covered up that can be a real pain to find later on.
Expect a massive mess when they texture the walls. Have everything covered in plastic, and put tarps over the plastic on the ground. Assume that they will NOT do a good job of doing this!!!!
If you are paying for each sheet, count how many you actually get delivered and how many are left over. Do not pay until they pick up the leftover sheets and they deduct the.cost of materials according to how many sheets they didnt use.
Be sure that they use 5/8s sheetrock on the ceilings. Half inch will sag on a ceiling over time.
Expect to have somebody with a criminal record in there at.some point. It's very common for felons to get a job doing this type of work. Dont leave anything of value out or in sight!!!
Be sure every sheet is mailed or screwed completely. With some crews, one guy will cut and install the sheetrock, a other will install all the screws or nails. I've seen several closets and small rooms that only had 4 nails in the sheet after they have been long gone.
Screws are better then nails, but nails are faster to get a sheet up, so it's common to have both in a sheet.
Have a roll of blue tape to mark issues. They hate this and might pull it down and pretend it wasnt there. Be sure to count how many places you marked with blue tape..
Once you pay them, you will find it very hard to get anybody to come back. This is when I get hired by people building a house for the first time. I've spent an entire week fixing issues and had to work around a stack of sheetrock 3 feet thick that they where charged for. That was the worse case. I've also been hired to clean up the mess that was left, including scraping joint compound off of the floors in every room and on the windows where the plastic came loose.