Bow needs to have all bow hair when playing middle to tip, and needs to
turn gradually so at the frog only the bow hair farthes from you is on
the string. To turn the bow, raise your wrist during an up bow
when approaching the frog, then lower it on the up bow to turn the bow
back to normal gain.
When moving from mddle to frog, raise your elbow slightly, then just
prior to frog, lower your elbow again. This helps to remove
excess weight on the bow during that time.
Also, on up-b ow when almost at the frog, use your fingers to
keep the bow moving while you are changing your arm direction of
movement. That way, it minimizes the time the bow is not moving
and smoothes the change of direction. Similar at the tip: use
your fingers to continue the down bow while preparing for the up
bow. It's not as pronounced at the end of the down bow.
At the end of a down bow, to start the up bow, squeeze with the end of
your third finger. That helps to start the up bow.
On up bow when approaching the frog, the bow should turn slightly out
of perpendiculat, with the frog a bit too much towards you, then near
the frog, straighten the bow out again. This will be just a few
degrees out of perpendicular.