The whole town, consisting of one main street and a several other site locations, is small and easily walked within a few hours.
However the little train is the easiest way to get around Calico Ghost Town and it is fun to ride. The breeze felt in the movement of the train certainly brought relief from the heat of the noon-day sun!
As I remember the engineer pointed out the interesting places and told the history of the town and it's mine. Well worth the time.
If your car is not in excellent condition, better borrow one. Mule or horse might be fun.
Okay, seriously, a car is the best way to get around this area. Make sure to have plenty of water for you and your car as overheating is always a threat in the desert.
Avoid going off the road, unless you have an ATV--all terrain vehicle--as the sand can be quite soft in areas and it is difficult to get a car out of a sand trap.
If a car is not possible for you then the best way of getting to Calico is by tour bus from your hotel.