In everyday practice, most writers make a limited number of errors in the basics, but repeat those errors often. Below is a list of frequently occurring errors and corrections with techniques to prevent them.
Claire Cook, in Line by Line: How to Improve Your Own Writing, states:
Errors in agreement, a singular subject matched to a plural verb or vice versa, do not reflect faulty arithmetic or an inadequate grasp of verb forms. If you made a mistake, you have . . . lost sight of what words go together. . . . To avoid errors in subject-verb agreement, you have to know how to pick out the subject for every verb you use and how to tell whether that subject is singular or plural.
Example of incorrect subject-verb agreement: Two NCOs and one officer is at the back of the bunker.
Corrected: Two NCOs and one officer are at the back of the bunker.
ProTip: Avoid writing inverted sentences, such as those beginning with there is and there are, because they require an increased effort to match subjects and verbs. So do longer sentences, in which writers tend to match the verb with the closest noun—sometimes incorrectly. Develop habits of analyzing sentences as you write, and write as economically as possible.