Just got my first RV, now what?

Do a thorough inspection and make a list of problems and prioritize them. Try all the electrical and run the A/C, fridge, heater, stove, water heater, etc. As gbopp said, the most important thing is the roof. If the drivetrain is in good shape and it doesn't leak, you can work around most everything else.

Ripping up the carpet and replacing the mattress is probably a good start. You'll be able to see any rotten flooring and old carpet can hold mold and make the rig stink.