flaps should be at popsistion 5 on a standard experienced pilot's 737, typical flight.
Typically based on weather and on the runway's length may they adjust the flaps, flaps also have an affect on the speed and climbing rate of an aircraft like the 737, as flaps are used to decrease speed and increase drag. This therfore has an antagonistic effect on speed and on climbing rate, as one increases the other decreases and viser verser.