During an illustration editor's review some mistakes are noticeably common, so here's a list of those ones which might help illustration contributors in their submissions.
Copyright - When creating any drawing, the contributor must keep in mind not to include any logo or any brand in their illustration. There are already tons of illustrations out there so there are chances that your work might also look alike ones that are already online.
Jaggies - Jagged lines or edges, usually this is due by poorly tracing or poorly auto tracing a hand drawn sketch. One cause is if an image had been scanned in low resolution then upsized before auto tracing it also produces jagged lines. Another cause is upsizing a non-vector image, whether while editing or in final export.
Banding - Usually seen in gradients, instead of a smooth transition you'll see abrupt separate colors from dark to lighter color changeover.
Spelling - This is common in images with text(s), cards, posters, brochures, infographics. Not all buyers downloads vector file, there are those who want ready to use images especially ones who are doing rush projects.
Blurriness - This are unclear images, or having not much detail. Too much anti-alias to smoothen the edges, and upsizing a raster image ruins details.
In copyrights, use your own ideas, and before submission use either google's image search (images.google.com) or tineye (tineye.com) to check if your work have lots of similarities to others. Spelling, before putting text(s) in your illustration, make sure you use a spellchecker, spellcheck.net is an example. For jaggies, banding, blurriness, images should be checked always at 100% then apply the needed revision before submission.
Thanks for this! As someone who is learning how to illustrate this is very helpful!