This is my take on hobo mittens. There are only a few steps to make a unique wrist warmer.
An old sweater or knee high socks. I found this sweater at the dollar store. How is that for a score!
sewing machine, and coordinating thread.
a few pins to mark your lines.
Some buttons or other embellishment.
Cut your sleeves to the desired length. You can make these long to your elbows, short and a little past your wrist, or anything in between. It's up to you.
Place your arm on the sleeve (with your thumb to the original seam of the sweater) to get an idea of where you are going to trim up your mitten. I had to make a pattern of my arm because I couldn't take pictures and hold my arm down at the same time. It might be easier for you to just make a pattern. You want the sleeve to cover your knuckles. Keep that in mind when you put your real, or paper arm on the sleeve. Place your pins to mark where you will begin sewing in and down the arm. Knit is stretchy, so I find it easier to sew and them trim away the excess.