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.