I do not leave a tail up for more than a week. I find that it starts to go the other way and mat or rub against itself and break off. I always wash the tail and spray show sheen on then let air dry. I find that putting up a wet tail crimps it real bad for one (looks silly at a show with the hair folded up the wrong way) but braiding the hair wet seems to lead to more breakage in my experience, plus putting the sock or bag on wet promotes bacterial and fungal growth and can lead to a flaky tail dock. I once had a boarder put a red nylon tail bag on her palomino's wet tail only to find her horse's tail turned pink as the dye from the bag bled through! I've also had clients leave a tail bag on for a long period of time (all winter) believing his tail would be super long next spring. Turns out that his tail hair mostly broke off and knotted up into a matted mess, plus it smelled like a foot. Once the tail is clean and dry, braid it starting at the base of the dock end. I like to gently separate a few strands of hair to leave out of the bag from the base of the dock because you may get a bit of breakage at the base of the tail, just from stress of the braid or sock ties, so if you leave a little hair out breakage wont show in the middle of the tail. I learned this while showing Arabians. In the off season we do not put tails up as it does require some extra maintenance.