People commonly do this exercise with a cable machine, but you can do it without one as long as you have a band and bar where you can hang it.
Double the band over the bar so that there are two handles for each hand. Grab the bands with a double underhand grip about shoulder-width apart.
Then think of it like a standing crunch. Round your back, contracting your anterior core and rolling your elbows past your midline. Doing it in a standing position carries over to more of your lifts.
Do 4 sets of 25-30 reps once or twice per week. Training the core with resistance has a huge carryover to your deadlift and will protect your lumbar when you're using maximal weights.
While waiting at the DMV for my moped license renewal form, I decided to kill some time with one of my favorite childhood pastimes. No, not chewing tobacco and throwing rocks at whores. I'm talking about that crazy little word game known as Mad Libs.