1. Number one 最重要的人（或事物）；最好的人（或事物）

e.g.: Many people consider themselves number one, the most important person.

很多人认为他们自己就是最好的，是最重要的一个人。

2. Look out for/Take care of number one 先为自己着想，照顾自己的利益，为自己打算

One and only 绝无仅有的；独一无二的；有名的

e.g.: They are always looking out for number one and taking care of number one. It is as if they are the one and only person on Earth.

他们总是先为自己着想，只关心自己的利益，就好像他们是地球上唯一的人。

3. Pull a fast one 欺骗，捣鬼

e.g.: Jim only won the game because he pulled a fast one on his opponent.

吉姆因为跟对手耍了手段，才贏了比賽。

4. One in a million百万分之一，凤毛麟角，百里挑一，佼佼者

e.g.: She's one in a million.

她是个百里挑一的人。

5. At one time 同时，曾经

e.g.: At one time we met frequently.

我们过去常见面。

6. Roll up into one 合为一体；兼于一身

e.g.: She is a great person -- kind, thoughtful and intelligent-- all good qualities rolled up into one.

她是个很优秀的女人——善良，体贴，聪慧——集所有可贵品质于一身。

7. One good turn deserves another. 善须善报；要以德报德；好人应得好报。

eg: If he does you a favor, you should do him a favor. One good turn deserves another.

如果他帮你的忙，那么你就应帮他的忙，以德报德嘛。

8. Be/go back to square one 退回起点，从头再来

e.g.: His papers were lost in the accident, so he had to go back to square one with the work.

他的论文在这次事故中弄丢了，只得从头再写。