Here is a good place to start:
Downloadable Dinghy Guides | MotorHome Magazine
Do not trust what the salesperson at the dealership tells you. Insist on seeing the owner's manual for the vehicle you are purchasing to make certain that it can be towed. Look for a section in the manual called "recreational towing" or similar. Also be aware that some options may change the ability to tow behind a motorhome.
Make certain the weight of the towed vehicle is within the capabilities of your motorhome.
Have a good braking system for the towed vehicle.
Many of us like to tow a Jeep Wrangler, as they only need a tow bar, baseplate, braking system and lighting hookup. There are numerous other choices available. Some vehicles will require a driveshaft disconnect, transmission fluid pump, etc.