I've never used scrunchies. I use the big friendly elastic thingies (Are they by Goody?). My hair isn't long enough to make a nice healthy pony puff so I just make a pulled-back puff.
I just comb my hair in a backward direction (Usually my hair had been in big plaits and is well moisturized with S Curl after a night of baggying). Then I wear the elastic thingy like a necklace as I smooth my hair back with my hands. Next I hold the elastic thingy at the front and holding it against my nape, I lift the front over my face and twist it to cross at my forehead.
Then I start to slide the cross back, making sure to keep it crossed firmly against my head by pulling tighter as I move it backward. By the time I get to the point where I need it to be, I have enough length in the loop I was holding to stretch it over the puff and double it up.
Alternatively, I create the cross over at the nape my lifting the front over my face to my hairline, then I cross over the back and use my fingers to slide the front back while I tighten it by pulling the cross part to keep it from slacking. This works better coz you can pull the cross over away from your hair so you're not getting strands caught in the cross. Once you have enough length, you loop it over your puff and double up.
If the elastic is too short to double up, you can create a bow by just tying a double knot.
Combing out the puff with a pick creates a nice round dome: