"Review copy for errors in grammar, punctuation, spelling.
Check the copy for readability, style, and agreement with editorial policy.
Flow correction, minor re-writing if required, content review to verify facts, dates, and statistics
and anything which makes the content interesting and informative enough to the readers."
I have US English level 3 proficiency and much of what's there quoted above, I believe, doesn't require much experience. However, I have started proofreading to the level of journal articles with established institutions. May be I am the person you see fit for your project. Regards.