Who should be proofreading journal articles? I try to have any manuscript proofread before submission to an academic journal, where proofreading typically involves checking/fixing the spelling, grammar and overall style in English.

This decision often involves somewhat difficult decisions to make on how best to proceed. Here I am interested in one particular dimension of the problem. How to select someone good to proofread an article for an academic outlet?
To proofread something, you need somebody who knows about the subject matter. They have to gain something too, doing the work just for "fun" doesn't cut it. So your best bet is a coauthor, a colleague who is willing to swap proofreads with you, someone in the research group (understanding what others are doing should be beneficial), even perhaps your advisor.