Communication between raspberry pi and arduino

Hello, I am busy with a school project where i am building a weather station with a raspberry pi as main computer and then the arduino as the slave, what is the best way to send data between the two, for example inputs the arduino receive. I would like to receive the data and then write it to a sql database.

what is the best way to send data between the two

Servos waving semaphore flags.

How much data? How often? Wired or wirelessly? How far?

Why are you using the Pi and the Arduino? Specifically, what role will each play?