I should outline the process step by step. Start with the basics: why 9x12 inches? Maybe that's a standard size for certain printing purposes or media. Then move into setting up the PSD in Photoshop. Important to mention resolution, bleed areas, and color modes. Design elements like layout, imagery, typography, and branding should be covered. Maybe include tips on using assets, like stock photos or graphic elements, and how to layer them.

Wait, the user might not know about the difference between web and print. So explaining that could be helpful. Also, emphasizing the importance of bleed if they're printing. They might not be aware of that. Including a sample layout could be useful, maybe with sections for artwork, title, artist name, barcode, etc.

I should also think about examples or case studies. Maybe a simple example of a 9x12 layout. Also, software tips: using grids, smart objects for scaling images, adjusting colors for print. Maybe some shortcuts in Photoshop that could speed up the process.

Need to ensure the language is clear and jargon is explained. Terms like bleed, CMYK, RGB, raster vs vector – explain briefly if necessary.

Finally, a conclusion encouraging the user to start creating, and maybe a call-to-action for sharing their designs. Also, remind them to proofread and test the design in different formats.

Wait, are there any common issues when resizing or scaling in Photoshop that could affect the final product? Maybe advise using high-resolution images to prevent pixelation. And suggest using vector graphics for text and logos for scalability.

Including a section on tools and resources: links to free fonts, textures, maybe online calculators for dimensions and bleed. Maybe mention using Adobe Stock for high-res images.