A good rule of thumb for pulling manes, if the mane is very thick leave it longer and if the mane is very thin it can be pulled a little shorter. Super thick manes can not be pulled to braiding length all at once. I recommend keeping up with it every 2-4 weeks. Pull only a few hairs at a time. It’s tedious, I know, but you don’t want your horse’s crest having huge chunks missing. If your horse’s or pony’s mane is getting braided, please, please, please never cut it! A common misconception is a mane “just needs to be short” to braid it but that is just not true.
I recommend taping your fingers for mane pulling and using a plastic comb or using just your fingers to pull. Never use a metal comb. The seam created when the metal combs are cast will cut the mane. Also check out Youtube. There are many great videos out there on mane pulling. And…if in doubt…let your braider pull it. Remember you can always take more hair out but you can’t put it back once it’s pulled.