Let me tell you a little secret about me.
让我告诉你个秘密。

通常在给别人意见时使用

Let me tell you a little secret about me. When I was a child, I wanted to be a movie star. I thought it was not easy, so I didn't try. But you need to know that nothing in life is easy.
给你讲个事儿，我小时候想成为电影明星，我觉得这可能挺难的，所以就没有去尝试。但是你必须知道，生活中没有易事。

Let me tell you a story
我给你讲个故事

通常是给人讲大道理

Let me tell you a story. One day I met a beautiful girl and she asked for my number. I didn't give it to her because I thought I was too poor to have a girlfriend.
我给你讲个故事吧。有一天我遇见了一个漂亮的姑娘。她管我要电话号码。我没有给她。因为我觉得我太穷了以致于没法找女朋友。

The next day I see her walking hand in hand with a bum. So sometimes you don't know what people value in you.
但第二天我就看见她跟一个流浪汉手牵手走在路上。所以呢，有时候你都不知道别人看重的是你的什么。

Life lesson
人生智慧

可以说：Here's a life lesson.
Let me tell you a life lesson.
I wanna share a life lesson with you.

Here's a life lesson. Never get in a fight with a crazy person no matter how strong you think you are. Crazy always beats strong.
分享个人生智慧给你。永远不要跟疯子打架，不管你觉得自己有多么强壮。因为疯狂永远比强壮厉害。

Share one's experience
分享经验

Susan shared her experience of love with me over coffee. One thing she said was to never waste your time in a relationship if the way you see someone changes for the worse.
喝咖啡的时候Susan跟我分享了她的爱情经验。如果你的他的看法变坏了，就不要再跟他浪费时间。

Something you can't learn in school
有些事情是在学校里学不到的

How to run a company is something you can't learn in school. You have to actually try it to see how it's done.
如何经营一家公司是你在学校里学不到的。你必须亲自尝试，然后了解如何做到。