I've been thinking about style and grammar lately. This is mainly because I want to write more regularly about good English and academic prose. In general, I prefer to approach the problem in terms of developing your style, not improving your grammar. Normally, grammatical mistakes are poor style, of course. Errors in verb agreement and punctuation is something you want to avoid if you want to impress your reader as a stylist. But I wonder how much a post on basic grammar can help.
For example, in Danish "er" (pronounced roughly like "air") means "is". So I will often find people writing, say,
Innovation are the key to the success of modern companies.
Well, that's wrong, of course. "Are" should be "is". But I think these authors understand how to conjugate the verb "to be". I think mistakes like this arise mainly out of carelessness.
So my goal, when working directly with authors, is to engage with their prose at the level of style. My aim is to get them to think about how they want to say things. Here the idea that a sentence may be poorly written because the author "isn't good at English" generally gets in the way. It is much more constructive to talk about what the author wants to say and then find ways of saying it effectively. The solution is rarely simply to turn an ungrammatical sentence into a grammatical one. We must turn an obscure sentence into a clear one.