Some trails are challenging, but most are fine for the average person and average vehicle. Just pick the ones that match your vehicle, equipment, and ability, but ALWAYS have a second, or more, vehicle with you.
Moab is a beautiful place, you will want to as many of the trails as possible, and bring that camera.
The best time to go is Sunday through Thursday, as the hotels are not as full. I show on my map, which ones have trailer parking, and where to park the trailer at various trail heads. You can ride your ATV on the streets in Moab, so I show which roads to take to trails you can get to from town.
There are Jeep and ATV jamborees in Moab. Check the Internet for the latest information.