I wish / if only:

Use of I wish / if only:

There are three distinct types of I wish / if only sentences:

Wish, wanting change for the present or future with the simple past.
Regret with the past perfect.
Complaints with would + verb.

Expressing a wish:

Form:
If only / I wish + simple past

Example:

If only I knew how to use a computer. (I don’t know how to use a computer and I would like to learn how to use it)

Use:

To express a wish in the present or in the future.
The simple past here is an unreal past.
When you use the verb to be the form is “were”.
Example:
I wish I were a millionaire!

Expressing regret:

Form:
If only / I wish + past perfect

Example:

If only I had woken up early. (I didn’t wake up early and I missed my bus.)

Use:

To express a regret.
The action is past.

Complaining:

Form:
I wish / if only + would + verb

Example:

I wish you wouldn't arrive so late all the time (I'm annoyed because you always come late and I want you to arrive on time)

Use:

To complain about a behaviour that you disapprove.
Expressing impatience, annoyance or dissatisfaction with a present action.