I wish / If only

1.- 'I wish / If only' + past simple 

(to express that we want a situation in the present or future to be different)

• I wish you were here.

2.- 'I wish / If only'  + past perfect 

(to express a regret, or that we want a situation in the past to be different)

• I wish I had studied harder for the exam.

3.- 'I wish / If only'  + would + V. 

(to express impatience, annoyance or dissatisfaction with a present action)

• If only you wouldn't smoke.