If only I didn't have to study English grammar ...

Use of I wish / if only:

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

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

See below for grammar explanation

Click here for practice 1

Click here for practice 2

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 behavior that you disapprove.
• Expressing impatience, annoyance or dissatisfaction with a present action.

Explanation from My English Pages