Yeah, Claude's right, it has to do with the wheel on the bottom left. You have to match the little circles, with the big circle. I think you need 3, or maybe 4 of them (not really sure). What I did when I really wanted to catch a monster, I waited until the big circle changed to an element which matched the arte that I had, and then I used the arte over and over again. I'm not 100% sure of this, but I think your chance of catching the monster increases if the element is the same element as the monster.