I use two thin hair bands to make a low hanging pony tail (bands sitting in the neck) and then dividing my hair into 3 somewhat equal strands. I throw the right strand to the front of my shoulder and when dividing the bulk into middle and left strand i throw the left strand over the other shoulder.
then i hold the middle strand with one hand and get one side to cross over. once that one cross over is done i hold it with the hand i got the side strand with to grab the right strand with the right hand.
that's ow i get it started.
once i've done 3-4 cross overs i turn my head all the way sideways so i can braid the remains in front of my chest/shoulder.
i ALWAYS stuff my braid straight down the back inside the jacket. the braid can't go down your spine cuz then it will bulk up in the neck leaving your head forced down.
having the braid come up to the front down your shoulder/chest left me with hair strands coming out of the braid and poking me irritatingly in the neck like bugs hitting me or fine needle pokes.
Since i got a layered hair cut i fixate the bangs and strands too short to stay in the ponytail with hair pins along the side of the head. On top they put too much pressure on my scalp with the helmet on.
it all just takes practise. i wasn't great at it but after a dozen times and practicing in front of the mirror with my arms getting to tired and heavy, I got it down now.
Sometimes tho i'd rather sweat in my helmet for 5min (gas stop) cuz most of the time my braid is falling apart at the base (neck area) and I have to redo it before putting the helmet on again.