I'm going to be replacing the rear passenger's side window regulator and motor in my son's 04 sedan. Does anyone have any tips or things I should look out for before starting? Any help would be great since I've never done this before. Thanks in advance!

Ben

 

Ben,
If you don't have a set of plastic trim tools, get one. They are inexpensive and worth their weight in gold for removing the trim panel without damaging it or scratching the paint of the door.
After you get the trim panel off. you'll need to remove the water dam. Using a single edged razor blade and/or an xacto knife, cut the bead of sealant that holds the water dam in place. Take your time and avoid damaging the dam itself. If you cut the bead more or less in half evenly around the whole water dam. the, you'll be able to stick it back on by matching the sealant line back up. It'll stick quite well.
The window glass needs to be in the up position to remove the regulator, but if it's not working, that shouldn't be a problem.
Make sure the motor is truly the source of the problem. You don't want to go through all that work to find out after you're done that the wiring or switch or something other than the regulator is where the fault is.