JiuZhaiGou is huge - but only the 'Y" shaped valley is created into the park we call JiuZhaiGou. The entrance is at the bottom of the 'Y', which is also the lowest point. It is about 8 km from the bottom to either top of the 'Y'.
In the park, there are coaches with drivers and in-coach guides who give running commentaries as the coaches move from scenic-point to scenic-point. You can hop-on/hop-off any coach at any scenic point. But a photo enthusiast would prefer to walk and look for vantage points to shoot. The wooden walkways are firm and safe. Walk whenever you can (but coach stops are always nearby).
Be prepared to spend at least 2 full days in the park even if it means breaking away from your tour group, there is so much to shoot. You can catch a taxi back to the hotel. Food, drinks and clean toilets are available in the park.
Download a JiuZhaiGou map or buy one at the entrance, Check out which are must-see scenes from the web or from books. I like the Wuhuahai Lake (Flowery Sea), Xinuihai (Rhinoceros Sea), Suzheng Waterfall, and Nuorilang Waterfall. But there are so many other beautiful sights in the park.
It can be very cold in December, so don't forget to bring thermal wear.
I travelled there on my own in 2004, Contact me if I can be of further help.