The first time I had to dress a mannequin was about 16 years ago at The Gap. I had no idea what I was doing and I'm pretty sure I stretched out the fabric of more than one "favorite tee". Luckily with the help of my peers and through experience, I figured out what worked best for me.
I'm not saying that there's a right or wrong way to dress a mannequin but this is the easiest way (and order) that I've found to work over the years. I also want to note that 6 days prior to when this video was filmed, I had surgery performed on my right hand (nothing serious, just a simple surgery to treat "trigger finger" but it still required stitches). I'm only mentioning that as additional proof that this is an easy way to dress a mannequin, because if I can do it with a busted hand, then you probably can too!
Also I realized afterwards that in the video I said it's a knit shirt but it's actually a woven (oops). Sometimes it's hard to dress mannequins and narrate at the same time!