Read the rules

• Use just in positive sentences to say that something has happened very recently.
• Put just before the main verb.

I have just phoned her.

• Use already in positive sentences to say that something has happened before now or earlier than expected.
• Put already before the main verb.

She has already read these books.

• Use yet in negative sentences and questions to ask if something (that you think is going to happen) has happened or to say it hasn't happened.
• Put yet at the end of a sentence.

— Has Tom been to a school disco yet?

— No, he hasn't been there yet.