Hello, 

Thank you for the kind words. The three moment common mistakes are typically: using which for that and that for which; using its for it's or it's for its; and not using a comma before a conjunction. Probably the most difficult area to edit are the references because most writers, I've noticed, do not properly follow the style guide (APA, Chicago, for example). I hope this helps! I believe I have posted examples of my work on this website. You can view them there. Best...