Rules for coreference resolution

I’m trying to understand how English tracks a subject between sentences. I believe the term is known as Coreference Resolution.

I’m wondering if there’s a base set of rules which can define coreference and anaphora resolution.

In general you can find the subject by using SVO

The subject in most sentences comes before the verb.

She loves him.

So in this case she is the subject, however if we add another sentence after.

She loves him. They are happy.

As you can see here the Subject of the next sentence They refers to the subject and object of the previous sentence.

Another example off the top of my head:

She loves him. It was a cold day out.

in this example the subject it doesn’t appear to have a relation to the previous sentence: I don’t even know what I could classify the subject as?

Just from these few examples I cannot determine a set of general rules. I don’t need to cover all the scenarios but I would like to find a way to cover the majority of use cases