1.一朝被蛇咬，十年怕井绳

Once bitten, twice shy.

2.一言既出，驷马难追

A word spoken is past recalling.

3.一箭双鵰/一举两得

Kill two birds with one stone.

4.一寸光阴一寸金

Time is money.

5.一失足成千古恨

The error committed on impulse may turn out to be the sorrow of a whole life.

6.一将功名万骨枯

What millions died that Caesar might be great.

7.一年之计在于春，一日之计在于晨

Plan your year in spring and your day at dawn.

8.一人难称百人意

You cannot please everyone.

9.一气呵成

Never make two bites of a cherry.

注：

on impulse：一时冲动，一时心血来潮

turn out：结果是， 证明是

10.一白遮三丑

A white complexion is powerful enough to hide seven faults.

11.一知半解

A little knowledge is a dangerous thing.

12.一心一意

undivided attention.

13.一丘之貉

These people are cut from the same cloth./are tarred with the same brush.

14.一目了然

His words just leap to the eye. Do you need me to explain it?

15.一帆风顺

go off without a hitch.

16.一刻千金

every time counts.

17.一事无成

I am happy to know that all have ended in smoke about him.

18.一败涂地

The outcome of the election just bit the dust.

19.一针见血

hit the right nail on the head.

注：

undivided attention：一心一意

go off：进行，响起，入睡，变质

without a hitch：顺利无阻地(轻易地)

bit the dust：倒下死去(一败涂地, 受辱)

comment on：对 ... 评论

20.一清二楚

as clear as crystal.

21.一落千丈

My son's schoolwork has gone to pot. He really lets me down.

22.一鸣惊人

come as a bombshell.

23.一诺千金

He never goes back on his word. He is as good as his word.

24.一时兴起

Don't always do things by fits and snatches.

25.一蹴可及

make it at one stroke.

26.一筹莫展

at wit's end.

27.一览无遗

be in full view.

28.一窍不通

What you said is all Greek to me. 

注：wit's end:技穷

29.一视同仁

He treats everyone across the board.

30.一模一样

These twins look as like as two peas.

31.一时兴起

on the spur of the moment.

32.九死一生

to have a hair-breadth escape

33.九牛一毛

a drop in the bucket.

34.人生如梦

Life is but a dream.

35.人生自古谁无死

Death comes to all men.

36.人生百岁古来稀

It is seldom that a man lives to be a hundred years old.

37.人定胜天

Man can conquer nature.

38.人不可貌相

Appearances are often deceptive./ Never judge a book by its cover. 

注：

across the board：包括一切地, 全面地

on the spur of the moment：一时冲动地, 立刻

a drop in the bucket：沧海一粟

conquer：征服，占领，战胜，得胜。

常用短语：

①divide and conquer：分步解决，分治 

②stoop to conquer： 降低自己的 身分去...