The Second Conditional:

(if + past simple, ... would + infinitive)
If I had a lot of money, I would travel around the world.

If clause and main clause

We use if + past to talk about an imaginary present or future situation (although the verb is in the past, the meaning is present or future). And we use would + infinitive to talk about the result or consequence of that imaginary situation.

• If we had a mansion in the country, we’d go there every weekend. 
• Would you travel around the world if you won the lottery?

Comma

When the if clause comes first, we usually put a comma after it. We don’t use a comma when the main clause comes first and the if clause comes second.

• If I won the lottery, I’d buy a mansion.
• I’d buy a mansion if I won the lottery. 

Would

Would/wouldn’t is the same for all persons.

• I/you/he/she/it/we/they would/wouldn’t do that if it was possible. 
• I‘d never tell anyone if you told me your secret. 
• I wouldn’t tell anyone if you told me your secret. 

Could

We can often use could + infinitive instead of would + infinitive in the main clause.

If you spoke English, you could get a better job.

Was or were?

In the second conditional, we can use if I/he/she/it were (more formal) instead of if I/he/she/it was (spoken English).

• If I were/was fit, I would run a marathon.
• We wouldn’t have any problems if he were/was more reasonable.

But we use were (NOT was) when we give advice with the expression if I were you.

• If I were you, I would stay home and rest.
• I wouldn’t pay any attention to what he says if I were you.