It is best to rosin the hair slowly begining at the frog. Quick rapid rubbing of the rosin will warm the area with a thick layer of melted rosin. This thick shiney surface will cause a poor tone which makes the musician think it needs more rosin. A thin even layer of rosin will produce the clearest sound.
A perfect test is to play a short peace, then with a bit of terry towel clean the strings and remove all the rosin from the hair, (until it stops squeeking) then play the same peace again. You should hear a clean sissle-free sound.
Now rosin with one stroke, slowly, from frog the head. Do the reverse the next time you think to apply rosin. (Head to frog)
Never was your hair. The internet is full of "techniques" for washing your hair. Mostly by urban legend bloggers.
All music is written for the bow, by kind to it.