Here's what I do for manes and tails and I'm growing just under 2 inches a month. I use a new product called BioMane. It is seriously amazing. A lot of barrel racers I know are using it and they love it (if barrel racers love it, it's got to be good) It's a feed. I order it off their website Home page. It is the greatest product I've used for growing manes and tails (and I've used a lot)
Mane: It's VERY important not to braid too tight at the base of the braid (near the roots) because this will cause irritation and result in rubbing. It's a constant pull on the hair. So I start the first few crosses of the braid fairly loose and then about halfway into it I tighten it up to make sure it holds. Don't use rubberbands to hold the braid if you're leaving it in. Band cut the hair strands if they're left in. Use black electrical tape. It's better than other tapes because it won't leave a gummy mess when you remove it.
Tail: Same thing goes for the tail when starting the braid, don't do it too tight. I start at the base of the tailbone, fairly loose for the first couple crosses and then tighten it up and finish with black electrical tape. I keep the tails in tail bags because the horse naturally is going to swat at flies, and this causes the hairs to break. But if the tail is in a tail bag, the hairs are protected. Really I think most any style tail bag works, just pick one that will fully cover the tail (the braided portion) and won't irritate your horse.
BRAIDING DOESN'T MAKE THE HAIR GROW! Braiding helps protect the hair. BioMane is what is making my horses' manes and tails grow. I braid them to ensure that what is growing is going to stay and not get broken off by swishing and swatting.