If you want to avoid undermining your credibility, there's two things to watch for in your writing: subjects and verbs.
What at first seems like a simple rule of grammar — singular subjects takes singular verbs and plural subjects takes plural verbs — quickly becomes complicated by special cases.
Here's a few of those exceptions:
1. Nouns ending in s
Some nouns ending in s such as news, lens and summons take singular verbs.
"The news from abroad is (not are) disturbing."
2. Nouns ending in ics
Many nouns ending in ics are singular or plural depending on how they're used. According to William Sabin's "The Gregg Reference Manual," "When they refer to a body of knowledge or a course of study, they are singular. When they refer to qualities or activities, they are plural."