For raster images, use full resolution images placed into the PSD document ( File > Place Embedded).
Use masks to crop images in the PSD document (Layer Masks / Vector Masks).
The developer will use this workflow to create the final images.
For example, naming layer “150% image-developer-story.jpg60%” will create a JPG saved at 60% quality sized to 150% of the size in the PSD. This example is just for your insight into the process – you do not need to name the layers this way, the developer will do this.
For vector images, link to the original .AI file.
Create separate asset files outside of the PSD file.
Create SVG files from AI files. The developer will do this.
Ensure all purchased assets are linked in the PSD file (replace FPO and watermarked images).
Ensure all the layer comps in the Layer Comps palette are up to date and accurate.