1. Singular + singular verb
The cat runs. Add ‑s to verb
2. Plural + plural verb
The cats run. no ‑s
3. Compound subjects (and)
Tom and Jerry are friends. plural
4. Or / Nor (closest subject)
Neither the coach nor the players are ready.
5. Intervening phrases
The box of chocolates is full. ignore "of chocolates"
6. Indefinite pronouns
Everyone is here. / Nobody knows. always singular
7. Collective nouns
The team is winning. (AmE) singular
8. Each / Every
Each student has a book. singular
9. Titles / names
The United States is large. singular
10. There is / are
There are many reasons. match noun after verb
11. Relative clauses
She is one of those who are talented. verb agrees with antecedent
12. Fractions / percentages
Half of the cake is gone. Half of the cookies are gone.