When I woke up this morning my girlfriend asked me, “Did you sleep good?” I said, “No, I made a few mistakes.”

—Steven Wright

Everyone struggles at one time or another with finding the right word to use. We’ve all sent out that email only to realize we typed there when we should have said their. How many times have you found yourself puzzling over the distinction between affect and effect or lay and lie? You can also find billboards, road signs, ads, and newspapers with usage errors such as these boldly printed for all to see:

Perhaps there is little need here to preach about the value of understanding how to correctly use words. Quite simply, in formal writing, conventions have been established to aid us in choosing the best term for the circumstances, and you must make it your business to learn the rules regarding the trickiest and most misused terms.

This PDF contains a list of several commonly confused words—as well as how to tell which word you should use.

You can also dig up style handbooks with recommendations on using tricky terminology within your discipline. For instance, Geowriting: A Guide to Writing, Editing, and Printing in Earth Science, by Robert Bates explains terms commonly used in the field; medical students can turn to The Aspen Guide to Effective Health Care Correspondence or Writing, Speaking, and Communication Skills for Health Professionals.

The Chicago Manual of Style answers almost every conceivable style question—it is essentially a bible for book publishers. Never hesitate to look up a term for its proper usage if you are uncertain—there is a lot to be said for being correct.