first, wax them with a REAL carnuba wax. A paste, not liquid. This helps prevent chips, and peeling. Before I started doing this, I had tons of problems with peeling. Thankfully, I got two replaced under warranty, and had a chance to start over. Kept waxing them very carefully(They scratch soooo easily), and just washed them with soap and water. LOTS of water, and a lamb skin mit. Do not use a brush or sponge...BAD idea. The wheels scratch easier then the paint on the car imho.
I only waxed the wheels maybe once every month or two. not often at all. helps with cleaning later on too as dirt doesn't stick so much, or brake dust.
Now, the 2003.5 wheels are a complete joy to own so far. Easy to clean, tougher paint too. No chipping yet, and no peeling. And when clean, I can use them like a mirror to shave for christ sake. Wild.