Much of my time the past few weeks has been occupied with copyediting, and I've kept a list of recurring errors and things that bugged me in the copy I've been editing. In no particular order:
The improper use of "insure" in place of "ensure."
The improper use of "draught" in place of "drought."
The improper use of "like" in place of "such as" or "for example." "Like" doesn't mean what many writers seem to think it means.
The improper use of "since" in place of "because." "Since" refers to a passage of time while "because" refers to a cause-and-effect relationship.
The use of phrases such as "be sure and" and "try and" when "be sure to" and "try to" would be more accurate.
The abuse of "etc." to end lists. This is a clear sign that the author hasn't completed his thought.