WISH & IF ONLY

Both used to express how we would like things to be different if we could change them. 
Both, same meaning, but if only is more emphatic.
They can be followed by another clause; tenses are relevant then.

1.  Would + infinitive.  Used:
                a. to complain about things you find irritating. (Subjects of subordinate clause and main                             clause must be different).   I wish my neighbours would spot arguing all day.
                                          
                b. for wishes for the future when we believe the action will probably not happen                                         (could can be used instead of would) I wish I could work for the new local company, (but                     I know I haven't got any chance due to lack of qualification, for instance). 

     2.  Past simple.
         to talk about things you would like to be different in the present, but which you view as being                  unlikely, impossible.

I wish I were stronger

         As in conditional sentences, we use were for all the grammatical persons. However was is also            possible (less formal)
  
     3. Past perfect.
         to show regret or criticism about things that happened or not in the past.

I wish I had studied Maths any harder. Too late now.

Pink Floyd and Wish you where here