Not just his shooting, his overall game needs to be improve. If his overall game improves, his shooting percentage will go up. He can't expect to shoot at a high percentage if he has trouble dribbling the ball and trying to create his own shots. Ariza usually starts off the game trying to create his own shot which isn't working very well. So most of the time, he starts off shooting terribly, then when he finally get set for the open three, his confidence is diminished due to all the missed shot he chucked up which trying to create it himself. Ariza has a lot to work on if he wants to become an all star caliber player.
Ariza will never be an allstar player. He is a 4th or 5th option at best, he's playing way too many minutes and taking way too many shots. Problem is there is no one else unless Buddinger and Taylor get more minutes.
The problem now is that he is not even making wide open shots, not only contested ones and ill-advised ones. Opposing team is just leaving him WIIIIIIIIIIIIIIIIIDE open and let him shoot...
the problem is he doesnt fit this role hes trying to play. he is just a horrible ball handler and cant shoot off the dribble, he is efficient spotting up and slashing to the basket and that should be hes focus on the offensive end.