Use WISH + PAST SIMPLE to express wishes about PRESENT situations that are NOT TRUE or IMPOSSIBLE to change right now. You want reality to be different. Structure: I wish + subject + PAST SIMPLE. Use WERE (not was) for all persons with 'be'.
Practice tip: Think: What's TRUE now that you want to be DIFFERENT? Use WISH + past simple. Reality opposite of wish: I'm poor → I wish I were rich!