bow stroke from frog through the midpoint and to the tip.
Between midpoint to tip, your elbow remains stationary.
It helps a lot to practice in front of a mirror.
Your bow should be perpendicular to the strings at the midpoint of the
bow. (recommendation to be ammended later)
Your upper and lower arm and bow should all be in the same plane.
(recommendation to be modified later.)
Your bow should rotate slightly between midpoint and frog so that at
the frog, not all the bow hair is touching the string, just the bow
hair farthest from you. Between frog and midpoint, the bow should
rotate back so all the bow hairs touch the strring, and remain that way
from midpoint to tip.
Your wrist should 'dip' as you approach the tip, to reduce stress on
the wrist.