Remove Schumacher, he'd fuck up anyway.
This above all else. Sadly, they wouldn't, given they kept him from Batman Forever in the first place and presumably this better film would make more money and be less of a critical lulzbomb.
I'm not really sure if we can avoid the trajectory the pre-2005 Batman movies were taking. They started out in Tim Burton's usual teenybopper-gothizied style and were lurching back to the tone of the Adam West series as is, along with the unpleasant homosexual innuedo most Batman megafanboys were afraid of appearing/being associated with the characters even, uh, pre-nipple batsuit. If Schumacher were to stay, and even with a "better" script, it would stay on that path.
Another director? I really don't know. Judging from the way some of these film proposals and potential directors look, I'm not sure the pre-2005 franchise can be saved. Even the best case scenario probably has it looking like the 1989 film in style all over again vs. the 2005 one.