Wikipedia defines colloquialism as a word, phrase, or paralanguage that is employed in conversational or informal language but not in formal speech or formal writing. In writing fiction, our colloquialisms are often those ways of putting our verbal speech into written language; perhaps the hardest to self-spot and edit.
For example, the romance novel I wrote had been through professional editing and it had been many months since I'd last read the whole book at once. My editing service had caught my idioms of "speech" in my writing and deleted them; such as, my southern way of saying "hollered" instead of screamed shrieked, or howled. But the service missed a more subtle one that I noticed when rereading my book. When describing emotional issues between characters, I was fond (too much so in places) of using the word "feel" and its derivatives.
I was already aware that in my personal letters, I was a "feeler" instead of a thinker; hence using feel/felt more often than think/thought. But, I was unaware it had filtered into my professional writing. After making my "slang" discovery, I quickly got out my Thesaurus and came up with more vivid words to express my characters' feelings.
I believe this is the most difficult self-editing task a writer can face. How many of us are aware of the many idioms, colloquialisms, and redundacies we use in everyday speech? The familiar "you know, um, or uh." For a southerner, common terms such as "reckon, fixin', and y'll." The same can apply to our writing.
The best advice I can give, is to put aside your work for as long as you can; the more days and weeks that separate you from your words, the easier it is to spot errors, no matter what kind. Also, get friends, a critique partner, or writers group to read over your material. Then, if needed, get a professional to check for mistakes of all types, including your own special way of expression - which may look redundant when examined from "afar".
© 1999 by Myra Nour