There are some additional facts that we need to be aware of and pay attention to. To begin with, there are a number of nouns whose plural forms do not include a plural -s. Particularly important examples for people writing academic prose include the following:
(1) phenomenon - phenomena, criterion - criteria, and formula - formulae
Relevant to mention in this context is also that there are nouns where both the singular and the plural form end in -s, such as the following:
(2) hypothesis - hypotheses, analysis - analyses, thesis - theses, parenthesis - parentheses
What all these words have in common when it comes to subject-verb agreement, is that the singular form takes singular agreement and the plural form takes plural agreement, regardless of whether the particular form in question happens to end in an -s or not.
The same goes for nouns that look the same in the singular and in the plural:
(3) sheep - sheep, hovercraft - hovercraft
and nouns that end in an -s, but happen to be uncountable and thus singular:
(4) news, aerobics, diabetes, and statistics (the subject).
Another fact that we need to pay attention to is that it is not always the case that we get plural agreement when two singular noun phrases are conjoined. If the two nouns are seen as forming a unit of some sort, normal plural agreement does not occur:
(5) [Bangers and mash] is my favourite dish.
(6) I will see to it that [law and order] prevails.
(7) [Egg and bacon] costs more than fried chicken nowadays.
In conclusion, in addition to knowing the rules stated above, you sometimes need a good dictionary to find out whether a certain noun that you want to use is countable or uncountable, and if it is countable, if it is regular or not, in order to get the agreement between the subject and the verb right.
You also need to understand that exceptional things may happen when noun phrases are conjoined. Sometimes the conjoined noun phrases are seen as referring to a unit, in which case we get singular agreement, but if the two noun phrases actually are seen as referring to two separate entities/substances of some sort, we get plural agreement (regardless of whether the nouns as such are countable or uncountable). The following two examples are intended to illustrate this last point:
(8) [Gin and tonic] is my favourite drink
(9) [Gin and tonic] are the two main ingredients in a gin and tonic.