Prepare
Downsample images to what print or screen actually needs: 300 dpi for the press, 150 for screens, 96 for the smallest file. Vectors and text are left alone.
The print preset keeps 300 dpi, which is what a press resolves.
Text and vector artwork are never rasterised.
Print, screen or smallest, with a size estimate before you download.
The defaults come from your file. Change a setting and the proof updates before you let go of the mouse.