Wish or If only

1. Wish / if only + would + infinitive

It is used to show complaints about a situation; the speaker also expects a change in the future.

For examples,

I wish you wouldn't arrive so late all the time. [You usually come late.]

I wish you wouldn’t drive so fast.[Drinking so much was not good, but you did drink.]

2. Wish / if only + past simple

It is used to show a state that a speaker is not satisfied with something presently and she wants to change it. For examples,

I wish the room were colder. [The room is hot.]

If only I was not fat, I would buy these clothes. [You are fat. The clothes do not fit you.]

3. Wish / if only + past perfect simple

It is used to express regret about past actions (the speaker wants to change the past). For examples,

I wish I hadn't drink so much. [I drank a lot then.]

If only I had studied hard, I would have passed the exams. [I didn't study hard, and I failed in the exams.]

NOTE: Wish + to do something = means "would like/ want" 

For example,

I wish to finish the assignment today. = I would like /want to finish the assignment today.