Hypothetical situations

Wish and if only
Wish or if only can express how we would like things to be different if we had the power to change them.

Present states
We use wish/if only + past simple to express wishes about present states. Stative verbs such as have, be, know and understand are used.
I wish I was/were smaller.
If only I knew how to play the guitar.

Present actions
We use wish/if only + would when we want something to happen or someone to do something. Active verbs (verbs describing action) are used.
I wish you would turn your music down.
If only this wind would stop blowing.
Wish/if only + would is used if we want to express irritation at other peoples' actions or behaviour.
I wish you would stop speaking.
Wish/if only + past simple can also be used if the actions occurs habitually.
I wish you didn't (or wouldn't) drink so much.

Present ability
Wish/if only + would is used for events which are outside of our control. Consequently, we do not normally say "I wish I would". Instead, we use "I wish I could" to indicate our inability  to change things.
I wish I could remember where I put my keys.

Wishes for the future
Wish/if only + would or could can be used to express wishes for the future. This use of wish suggests that the action will probably not happen.
I wish I could go on holiday with you in winter. (I know that I can't go with you)
If there is more possibility that the action will happen, we use hope.
I hope I can go on holiday with you in winter. (I don't know if I can or not)

Past situations
We use wish/if only + past perfect to express wishes and regrets about the past.
I wish I hadn't left school when I was 15.
The following structures can also be used to express wishes and regrets about the past: Third and mixed conditionals (If I hadn't been so tired, this wouldn't have happened.); Should have + past participle (We should have got the train. This traffic is awful.)

Would rather
We use would rather + past simple when we want someone else to do something in the present or future.
I would rather you start to study now.
If the subject of would rather and the following verb is the same, we usually use the infintive without to.
We would rather sit in the garden than go to the city centre.

It's time 
We use it's (high/about) time + past simple when we want something to happen or be done now. It implies that the action should have been done already.
It's time you went to the Hospital.