Since there are many different sensors, and they may use different communication protocols, there doesn’t exist one procedure that can universally handle all sensor inputs. What type of sensors do you have in mind? Analog? Digital? I2C, SPI?
The firmware has built-in support for rain sensor, which can be thought of as a simple digital sensor. It basically checks the rain sensor status inside the inner loop and performs actions accordingly. You can use this as a starting example to add additional sensors.