Hello! It's great to know that you're planning a trip to China - covering Beijing, Nanjing, Shanghai, and Hangzhou. Here are some travel tips to make your journey smooth and enjoyable.

Best Time to Visit:
The best time to visit these cities in China is during spring (April to June) and autumn (September to October) when the weather is comfortable. However, as these are also peak tourist seasons, prepare for larger crowds at tourist spots.

Route and Accessibility:
China has an extensive air and rail network, making these cities easily accessible. Start with Beijing, and then you can take high-speed trains to Nanjing, Shanghai, and Hangzhou, in sequence. The high-speed rail systems in China are efficient, convenient, and punctual.

Accommodation and Booking:
There are plenty of accommodation options ranging from luxury hotels to budget hostels in all these cities. It's highly recommended to book them in advance, especially during peak seasons. Websites like Booking.com and Agoda are quite popular for booking accommodation in China.

Clothing and Essentials:
Given you'll be traveling during possibly comfortable weather periods, pack lightweight, breathable clothing, along with comfortable shoes for walking. Don't forget essentials like travel adapters (China uses type A, C, and I plugs), sunscreen, and a good quality pollution mask for areas with high air pollution.

Health and Safety:
Ensure you're up-to-date with routine vaccinations before your trip. Avoid tap water - it's advisable to drink only bottled water. Maintain good hygiene, and stay aware of your surroundings to avoid petty theft.

Local Etiquette and Respect:
China is a country with a deep-rooted culture and traditions. It's important to respect local customs. Tipping is usually not expected and public display of affection can be frowned upon. When visiting temples or sacred places, dress modestly.