I have a fairly good grasp of Chinese, Korean, Spanish and Polish grammar, which is more useful from an editing perspective than is my degree in English.
To give you some perspective on understanding identification of first language sourced errors, I would like to share my experience in editing a PhD dissertation by a student at the University of Beijing, whose first language was Mandarin. The discipline was Economics and the topic was The Banking System in China.
The dissertation was twelve pages long. I found twelve minor errors, such as an occasional omission of a definite or indefinite article and that sort of thing. However, in the final paragraph, the writer had used a negative construction incorrectly.
Although, I did not profess to understand every aspect of what the candidate had written I did notice that the negative was used incorrectly. Why? Simplistically, the negative in English must agree with the verb. but in Chinese it agrees with the sentence. In Chinese you can say, in effect, I not like it too. In English that becomes I do not like it either.
I did not change the negative. I merely flagged it and advised the candidate to rewrite the sentence.
You should apply a cost benefit analysis to all of your major writing assignments. My analysis has led me to believe that ten minutes diligent editing is worth one hour of writing. The moment, you reach the stage where you have the bulk of your first draft done, you should seriously considering doing a major edit. The first thing you have to do is get out of your own way.
The secret of editing success is to do short edits on the screen and major edits on hard copy using a ruler. Why? The reason has to do with your bi-lateral brain. When you are writing you are in the sound mode and when you are editing you should be in the symbol mode. The ruler slows down your reading so that you are able to stay focussed on the symbols and do not drift off into the reading mode where you are converting symbols to sounds in your head.
What is Open Edit?
I'll be glad to answer that. If you wish to send me a piece of your writing for editing, be it an essay, a paragraph or two on whatever topic I will edit it and post both your submission and my editing on the Open Edit page under your first name or a nom de plume. Once that has been done, anyone who wishes to can download the item and re-edit it and I will post the second edit and any subsequent edits. If you really want to improve your writing skills concentrate on editing.