Conditionals and wishes

We tend to use 'wish' or 'if only' when we talk about something we want to be different, something that we would like to change but it's difficult or impossible to change.

Present

wish followed by  were

if only followed by  were

We use 'were' and not 'was' when expressing a wish or regret in the present.

I wish the weather were warmer.

If only it weren't raining.

We use wish followed by  would to describe things which annoy you.

I wish you wouldn't smoke while we're having breakfast.

Past

wish followed by the past perfect

if only followed by the past perfect

Expressing regrets in the past.

I wish I had studied harder when I was at school.
If only I had passed my exams.

 Simplified note:

• When we are talking about the present, we normally use 'wish' or 'if only' and the past simple. 
• If we are talking about things people do which annoy us, we use 'wish' and 'would'. 
• When we are talking about the past, we use 'wish' or 'if only' and the past perfect.

(reference: Self Study by British Council)