Sure, these are stunningly beautiful places in China with breathtaking views, here are some travel tips for your trip:

Best Time to Visit:
Huangshan:
April-May & September-November:
pleasant temperature, less rainfall, good weather.
Zhangjiajie:
It is less crowded during late March to early April and late October to early November, also the colors are stunning during these times.
Jiuzhaigou:
September to early November is the best time to visit due to the charming autumn colors, a cool temperature, and less crowd.

Route and Accessibility:
Huangshan:
Easily accessible either by bullet train from Shanghai or Beijing, or by flight from Beijing, Shanghai, Xian and other major cities to Tunxi. Then, buses take you to Huangshan Mountain.
Zhangjiajie:
You can take a train or flight to Zhangjiajie from major cities in China.
Jiuzhaigou:
Direct flights available from Chengdu to Jiuzhai Huanglong Airport, then you can reach Jiuzhaigou by public transportation.

Altitude and Acclimatization:
Jiuzhaigou is high altitude area, while Huangshan & Zhangjiajie are of moderate altitude. It’s not usually a problem for visitors, just keep your activities slower at the beginning to acclimatize yourself.

Accommodation and Booking:
Many hotels can be found at the base of Huangshan and Zhangjiajie while in Jiuzhaigou, it's advised to book in advance especially during peak season.

Clothing and Essentials:
Pack multi-layer clothing since temperature can vary greatly. You should also bring sun block, hat, comfortable hiking shoes and a waterproof bag to protect your camera.

Health and Safety:
Stay hydrated and bring along minor medications. Watch your step while walking and hiking to avoid any accidents.

Local Etiquette and Respect:
Be respectful to the local customs and environment. Do not litter or vandalize the places as they are UNESCO protected sites.