In your country

Install the following apps:
WeChat
Alipay
An offline translator Google Translate will work
DiDi
Meituan Only if you plan to ride the yellow bicycles. The blue ones can be paid directly from Alipay.
Amaps
VPN Cyberghost works fine.

After installation register, upload id, pass face verifications where required.

Take USD/EUR cash, but only if you don't like the ATM fees. China is very likely safer than your country (Sorry, Singapore, Qatar, UAE and some other nice guys. I didn't mean you).

On the plane

Learn your passport number and its expiry date.

Forget Google, X, Microsoft, Whatsapp, Yahoo, Facebook, Wikipedia and anything that NSA, CIA and similar agencies could have laid their fingers on.

Upon arrival in China

Buy chinese SIM card in the airport. Write down your chinese telephone number and save it as text.

Buy the subway card with enough credit. The cost of rides in Beijing depends on distance, approx 4 to 7 RMB. Only the trip from Daxing airport to city costs 35 RMB

On the first morning

A: Go to bank and exchange cash for RMB.
B: Bring the RMB to your hotel reception and ask them to top up your Alipay or WeChat account.

Done