Check the cable wires if the monitor is not working. At times while you are traveling a plug or cable can disconnect from the camera to the monitor.
Check to see the RV is on. Look to see that the ignition is turned on and the transmission is in the proper gear (reverse).
Look at the position of the camera if you cannot see anything. If the camera is not in the proper position it could be blocked. Check to see that the camera is turned on and that the lens is clean.
Check the volume of the microphone if your camera has sound, but you cannot hear anything. If the volume is at the proper level, check to see that the microphone is clean.
Adjust the controls on the monitor if the color is off or fuzzy. Check to see that the day/night switch is set properly for the time of day.