If two infinitives are separated by and they take the plural form of the verb.
To walk and to chew gum require great skill.

When gerunds are used as the subject of a sentence they take the singular verb form of the verb.
Standing in the water was a bad idea.

When gerunds are linked by and they take the plural form.
Swimming in the ocean and playing drums are my hobbies.

Most indefinite pronouns typically take singular verbs.
Everybody wants to be loved.

Except for the pronouns (few, many, several, both) that always take the plural form.
Few were left alive after the flood.

When noun and pronoun subjects like some, half, none, more, all, etc. are followed by a prepositional phrase, the object of the preposition determines the form of the verb.
All of the pizza is gone.
All of the pizzas are gone.

Use a singular verb form for units of measurement.
Four quarts of oil was required to get the car running.

Two singular subjects separated by or, nor, neither/nor, either/or, and not only/but also, use a singular verb:

Two plural subjects separated by or, nor, neither/nor, either/or, and not only/but also, use a plural verb:

One singular subject and one plural subject separated by or, nor, neither/nor, either/or, and not only/but also, use a verb that agrees with the closest subject (try to put the plural subject last):

Most of the time two subjects joined by and use a plural verb:
Jack and Jill went up the hill.

If each, every or no come before the subject, use a singular verb:
No pink and yellow is allowed.
Every boy and girl is welcome.

If the two subjects separated by and are really one item, use a singular verb:
Macaroni and cheese is my favorite casserole.

A singular subject needs a singular verb:
  The king sings when he is happy.

A plural subject needs a plural verb:
  The kings sing when they are happy.

Don’t be confused by intervening words:
  The king, living in that big castle, sings when he is happy.
  The king, along with the queen, sings when he is happy.
  The kings, living in those big castles, sing when they are happy.

Don’t be confused by an intervening prepositional phrases:
  The king of England sings when he is happy.
  All kings of England sing when they are happy.

I was proofreading and ran across a tricky subject-verb agreement issue.
I need to review those rules so will go through them one at a time in the coming days.

I will be referencing the following in my research:
YourDictionary.com (20 rules with one example each)
Townson.edu (self-teaching with diagrams)
GrammarBook.com (14 rules with examples)
Grammar.QuickAndDirtyTips.com (tips)

I need more time to prepare this blog posts series so will work on that tomorrow.

For now here are two procrastination quotes:
Never put off till tomorrow what you can do today. ~ Thomas Jefferson
Never put off until tomorrow what you can do the day after tomorrow. ~Mark Twain