Camera Ready Art

I'm looking for a link or tutorial that will help me with creating camera ready art in photoshop. I need to know how to make/save designs with 200-300 dpi.

Thanks!

To change the DPI, simply go to Image > Image Size and change it. But I've read that you would need like 1000DPI for camera ready art? Maybe I misunderstood it or something. Or maybe it's for professional use..

I have no tutorials, but you could always try to google for it. :)