Already is often used to add emphasis or to suggest that it is surprising that something has happened so soon. They were already eating their lunch. If you say that something is still happening or is still the case, you are usually emphasising your surprise that it has been happening or has been the case for so long. She was still looking at me... There are still plenty of horses round here. You use yet in negative sentences and in questions. It is often used to add emphasis, to suggest surprise that something has not happened, or to say that it will happen later. Have you seen it yet?... The troops could not yet see the shore... It isn't dark yet. In British English, already and yet are usually used with the present perfect tense. I have already started knitting baby clothes... Have they said sorry yet? In American English, a past tense is commonly used. She already told the neighbors not to come... I didn't get any sleep yet. This usage is becoming more common in British English.

already常用于强调或暗示某件事的发生快得令人惊奇：They were already eating their lunch（他们已经在吃午饭了）。still可用来强调对某件事发生或持续如此长时间感到惊奇：She was still looking at me（她还在看着我），There are still plenty of horses round here（这附近还有很多匹马）。yet常用在否定句和疑问句中表示强调，或对某事还未发生表示惊奇，或表示某事将要发生：Have you seen it yet（你看过了吗），The troops could not yet see the shore（部队还是看不见海岸），It isn't dark yet（天色还没有暗下来）。英国英语中already和yet通常用于现在完成时：I have already started knitting baby clothes(我已经开始织婴儿衣服了），Have they said sorry yet（他们道过歉了吗）。美国英语中，常用于过去时：She already told the neighbors not to come（她已经告诉邻居们别来了），I didn't get any sleep yet（我还没合过眼）。这种用法在英国英语中也越来越普遍。