Situation: My sister is untidy. (Verb "to be" in the present simple) Wish:I wish she was tidier. (Verb "to be" in past simple)
Situation: I am going to London next week. (Verb "to go" in present continuous) Wish: "I wish I wasn't going to London next week." (Verb "to go" in past continuous)
Situation: I haven't studied for the English test. (Verb "to study" in present perfect)Wish: "I wish I had studied for the English test." (Verb "to study" in past perfect)
Grammar and Tenses
Wish and past situations
Situation: I didn't go on holiday this year. (Verb "to go" is in past simple)Wish: "I wish I had gone on holiday this year. (Verb "to go" is in past perfect.)
Grammar and Tenses
Wish with modal verbs
With could to refer to ability
Situation: I can't play a musical instrument. Wish: "I wish I could play a musical instrument."
With would to refer to habits and free will
Situation: He whistles in the office. Wish: I wish he wouldn't whistle in the office. (In this sentence you are stressing the fact he wants to whistle and makes a habit of it.)
Grammar and Tenses
You could also say: "I wish he didn't whistle in the office." (In this sentence you aren't stressing his desire to whistle, but you are just making a comment about a present situation.)