I also recommend using the slow & controlled eccentric phase.
As mentioned above, the slow "negative" is easier on the elbows, but - especially when getting acclimated to this exercise - it also helps avoid banging your head on the bar as it travels underneath. That part also requires a certain knack, as you'll see many trainers execute an odd looking German shepherd-type head tilt to clear the bar.
Practice will eventually eliminate the need for this as you learn the proper body alignment, including foot position and pelvic tilt.