Was or Were, and when?

I know the distinction between 'was' and 'were' in this context:

I/He/She was angry at the time, but now I'm/he's/she's over it.

We/They were angry at the time, but now we're/they're over it.

However, I'm having difficulty in understanding 'was' and 'were' in the following examples:

- I wish I was/were dead.

- If I was/were to win the lottery, I'd probably buy a ferrari.

- If she was/were there on time, she could've called the fire brigade and saved our belongings.

- If she wasn't/weren't here, where on earth was she?

- Frankly, he had an incredulous look on his face, as if I was/were telling him that I'd been attacked by a band of goblins.

And so on and so on...

What's the deal with this? How does one (easily) learn to understand how to distinguish one from the other in such cases?

Comments appreciated.

[Casiopea]

From § 61. subjunctive. 1. Grammar. The American Heritage Book of English Usage. 1996

if clauses—the traditional rules. According to traditional rules, you use the subjunctive to describe an occurrence that you have presupposed to be contrary to fact:

if I were ten years younger,
if America were still a British Colony.

The verb in the main clause of these sentences must then contain the verb would or (less frequently) should:

If I were ten years younger, I would consider entering the marathon.

If America were still a British colony, we would all be drinking tea in the afternoon.

When the situation described by the if clause is not presupposed to be false, however, that clause must contain an indicative verb. The form of verb in the main clause will depend on your intended meaning:

If Hamlet was really written by Marlowe, as many have argued, then we have underestimated Marlowe’s genius.

If Kevin was out all day, then it makes sense that he couldn’t answer the phone. 7

Remember, just because the modal verb would appears in the main clause, this doesn't mean that the verb in the if clause must be in the subjunctive if the content of that clause is not presupposed to be false:

If I was (not were) to accept their offer—which I’m still considering—I would have to start the new job on May 2.

He would always call her from the office if he was (not were) going to be late for dinner.