1.let sb. in on sth. 要告诉某人一个秘密或讯息（很少人知道的）
I'll let you in on a little secret –Sarah only got the job because she's dating the boss' brother.
2. let's shake on it 协议达成；一言为定；那就这么合作吧
“How much for your bike?”
“I'll give you $100 for it.”
“How about $150?”
“All right. Let's shake on it.“
3. letit slide 不要在意这些小问题
I made some punctuation mistakes inmy essay, but the teacher let it slide – she didn't take any points off.
我在文章中犯了一些标点符号的错误，但是老师没有在意这些问题 － 她没有指出来。
4. let it go = let go 让它过去；放手；不再为此纠结
I was angry about what she did for along time, but eventually I decided to let it go.
5. let it be 顺其自然
“I'm not sure the oven is hot enough… maybe I should turn up the temperature.”
“Just let it be – the chicken is supposed to cook slowly, on low heat.”
6. let your guard down 放下你的防备
“After a series of terrible relationships, I was finally able to let my guard down after I got to know my husband.”
7. let's call it a day 今天就到此为止；今天的工作结束了。
We've already packed 30 boxes. I'm tired – let's call it a day.