1.already的用法：
(1)译作“已经”,通常用于完成时的肯定句中.如 I have already read the book./ Some visitors have come already.位置：通常放在助动词后,过去分词前或句尾.
(2)有时already也可用于疑问句中,表示惊讶或明知故问等感情色彩.如 Has the little boy has already got home alone?(惊讶) / Has he forgotten everything already?(明知故问)
(3)在陈述客观事实的情况下,already也可用于一般现在时或一般过去时.如 He is/was already a middle school student.
2.yet的用法：
(1)译作“已经”,通常用于完成时疑问句中.如 Have you cleaned the room yet?位置：句尾.
(2)译作“还”,通常用于完成时否定句中.如 I haven’t brushed my teeth yet.位置：句尾.
(3)还可用作conj.,译作“然而”.如 Though she was very tired,yet she didn’t want to give up.位置：并列句的后一个分句的句首.
3.just的用法：
(1)译作“刚刚”,通常用于完成时中.如 My father has just come back from work.位置：放在助动词后,过去分词前.
区别：just和just now：just now译作“刚才”,用于一般过去时.位置：句尾.同义词组：a moment ago.如 He drank some water just now.
(2)还可用作adv.译作“正好；仅仅”.如 It’ s just five o’clock./ Don’t be angry with him,he’s just a little child.位置：助v.系v.情v.后,实义动词前.
(3)还可用作adj.译作“正直的；公正的”.如 He’s a just man./ The result is very just.
希望我的回答能够帮到你,