If they need advice about punctuation I refer them to Noah Lukeman's The Art of Punctuation (A Dash of Style in the U.S.).
If it's grammar, spelling or syntax then I move on, leaving other writers to pile in with their helpful suggestions to consult Lynne Truss's remarkably successful Eats, Shoots and Leaves.
I hesitate to recommend Fowler's Modern English Usage for fear it may intimidate. If all you really want to know, right now, this second, are the correct uses of 'lay' and 'lie', then Fowler's is not your best immediate ally.
When using Fowler's you can be too easily sidetracked chasing up references. It's all very diverting, and very educative, but when you have a job to do, a deadline to meet ...
As in a street brawl - you need additional brawn, not brains, at that tense, eyeballing moment when you want to avoid a scrap. Fowler's is your trainer, your coach, not your sidekick. Fowler's will talk you through six rounds of a sparring bout, but will not come to your aid on Las Ramblas at 2.45 a.m. when confronted with a bottle-wielding drunk.
With Correct English you can get in, get it, get out, and get on with whatever is you're working on.
If you don't need a micro-treatise on a, b and c, and you need to know x, y and z, right here, right now, then Correct English is a guide to have within easy reach of the desk.
Unlike Fowler's, Correct English is unafraid to discuss regional variants; it contains a succinct couple of pages on "Scotch, Scottish, Scots", and examples of Yorkshire usage.
And, if you're keen to practice, Correct English contains a useful series of tests on grammar, punctuation, spelling and vocabulary.
Do not be tricked by its lack of a respected colophon, or its seeming 'Ingerlish for Dummies' appearance, Correct English is a useful tool.
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