they are pretty hard so go a little lighter at first,concentrate on the movement and make sure you dont move your feet at all, once you get it down, add more weight, if you do them with dumbells or barbells, they work well also that way
well no matter what thebench is like, just go from the other side. i go to two different gyms with 2 totally different types of preacher curls, and i can do them on both of them. for some you have to turn around the arm rest, others you can and have to go grom the opposite side.