Arithmetic: Do all the numbers make sense, both from the arithmetic point of view and for design consistency? Do the numbers in the schematic match calculated measurements based on gauge and stitch/row count?
Sizing: Do your sizes make sense given the standard sizes (CYC or otherwise) and the amount of ease desired? Do all pieces have instructions for all sizes?
Consistency: Do you use the same language to describe similar steps? Do you consistently use the same abbreviations, capitalization, grammar, etc.?
Charts and Schematics: Do these agree with the written instructions? Do they have all the appropriate notations, keys, etc.? Are they placed appropriately relative to the text?
Photos and sketches: Do these make sense with the pattern? Does the written pattern correspond with what's showing in the photo? Could a different pose or angle give a better understanding of the pattern's final look?
Flow: Does each section make sense following the last one?
Agreement with pattern norms: Do you follow your internal style? Does the pattern have all of the standard elements of a knitting pattern?
Copy editing: Typos, formatting, etc. not covered by the above.
Layout design: General comments about how the pattern fits together. I can also mock up a basic pattern layout for you, if you need that level of service.