Should I submit my artwork as single pages or spreads?

Yes, however, you should not confuse one with the other. A spread extends across two separate pages (or multiple separate pages) and should be designed as such within your design software. Single pages are exactly what you think they are—single pages or two-sided pages--but also require your design software setup properly (crops, margins, bleeds, 300 dpi images, etc.)

NOTE: Be wary of multiple spreads within a booklet—there is a difference between a print layout and a printer spread layout based on how many pages your book will be. We can explain this better over a quick call rather than write it down—it’s printer-thinking that formats pages based on their location in a book or booklet.