Here's my $.02

in addition to some of the tips you've already received -

After you make your loose wraps and when you begin to increase tension, make sure you tightly pinch the hair between your fingers (while also holding the shank of the hook) to help hold the hair in place

Make sure you are spinning the dubbing on the right direction (clockwise for right-handed tier)

For the flies I tie (mostly 14 and smaller) if I cut a bundle of hair and twist it, the diameter of the hair should be about twice the diameter of the hook's eye