How hard can it be to run through a manuscript and check for spelling and grammar errors? Well, harder than you think; or at least much more time consuming than you think…
A few tips:
1) Save your MS in a different font and a larger size, and look through it again. Apostrophe and inverted comma mistakes especially show up better in a font like Times Roman compared to Ariel.
2) Invest in a style guide. Do you really know when to put a full stop outside of a closing bracket and when to put it inside? What is the difference between writing ‘the 1960s’ and ‘the Sixties?’ Look for the answers in something like the Oxford Guide to Style (Oxford University Press). If you don’t want to buy it, look in your local library or your nearest university library.
3) Make good use of spell checks, but of course bear in mind that the spell checker will not identify an error such as writing ‘there’ when you meant to put ‘their.’
4) If you can afford it, seriously consider employing a professional. Nothing looks more amateurish than a book full of errors, whether they come from your own manuscript, or from glitches in the typesetting process. If you can’t afford a professional, get as many very literate friends as possible to help your out. You and they will discover more errors than you expected!
I like point one the best, but if in doubt, get a proofreader. I would get one anyway!