行将就木；奄奄一息；生命垂危
at death's door
We were very surprised to hear that our favorite teacher was at death's door.

 
老调重弹
harp on one (or the same) string
I've already told you many times that I have no money to lend you. I wish you'd stop harping on the same string.

 
多此一举；徒劳无益
carry coals to Newcastle
To offer him money is to carry coals to Newcastle; he is very wealthy.

妄自尊大；自以为了不起
too big for one's boots
John is too big for his boots; that's his trouble.

 
守口如瓶
keep a quiet/still tongue (in one's head)
You'll keep a quiet tongue in your head, will you?

 
充耳不闻
stop one's ears; turn a deaf ear
He stopped his ears to bad news.
The president always turns a deaf ear to people's complaints.

光阴似箭；岁月易逝
time flies
Scientists prove time flies when you're busy.

先发制人；比...抢先一步
steal a march on (someone)
The company plans to steal a march on its competitors by offering the same computer at a lower price.

 
夸夸其谈；信口开河；信口雌黄
shoot off one's mouth
It seems like every senior official in the administration is free to shoot off his mouth on any subjects at any time.

血浓于水
blood is thicker than water
He gave his brother a good job because blood is thicker than water.

 
百闻不如一见；眼见为凭
To see is to believe; Seeing is believing
To see is to believe? No, eyes can be easily deceived.

 
全力以赴
do one's level best; go all out; go great guns; pull out all the stops; put one's best foot forward
I did my level best to help him.
I will go great guns for the team.
Don't worry too much about the TOEFL iBT test. Just put your best foot forward and do what you can!

早起的鸟儿有虫吃
the early bird catches the worm
Remember, it's the early bird catches the worm - you should try to get to it early.

 
有志者事竟成
where there is a will there is a way
In the writing test, John concluded his essay by writing "where there is a will there is a way."

 
有其父必有其子
like father/mother, like son/daughter 
A good example of "like father, like son" is George Bush and George W. Bush.

安如盘石；十分平稳
(as) steady as a rock
As he aimed the gun, his hand was as steady as a rock.

 
安然无恙
safe and sound
All his sons returned safe and sound from the war.

附注："safe and sound" 的发音并不是一个字一个字念，而是将 and 中的 "d" 不发音，并将 "an" 与其前面的子音 (在此为 safe 中的 "f") 连音，所以实际的读音是 "sa - fan - sound"。英文有不少类似 "safe and sound" 这种使用两个词性相同的字、中间用 and 连接起来的固定搭配，它们有些有连字符，有些没有，但不管有无连字符，它们实际的读音大多如上述，如 "cloak-and-dagger"、"hard-and-fast"、"ins and outs"、"up and about"、"spick-and-span" 等等；当然啦，如果 "and" 前面那个字的字尾是元音，那么就不会有这种连音的情况发生。读者若能把握这原则，并勤加练习，对于听力的提升也会有所帮助的。这种固定搭配在英文中叫做 "binomial"。

名副其实
worth (or worthy of) the name
No policeman worth the name should ever let a criminal escape so easily.

 
如坐针毡；坐立不安；焦躁不安；如热锅上的蚂蚁
like a cat on hot bricks (英) / like a cat on a hot tin roof (美); on pins and needles
She was like a cat on hot bricks before her wedding ceremony.
I was on pins and needles all day until she called me.

如意算盘；痴心妄想；一厢情愿
wishful thinking
Their hopes of a peace settlement are nothing more than wishful thinking.

因小失大
spoil the ship for a ha'porth o'tar
I'm going to buy some new paint brushes -- all the old ones have gone stiff. I've paid a lot for the paint and I don't want to spoil the ship for a ha'porth o'tar.

附注：这句成语中，ha'porth = halfpennyworth，o'tar = of tar。它原来是写成 "spoil the sheep for a ha'porth of tar"，即「不愿花半便士买焦油医治羊伤而导致羊死亡」。有些地方将 sheep 的音发成 ship。

自吹自擂；自我吹嘘
blow one's own trumpet/horn
She's very good at blowing  her own trumpet.

自取灭亡；自掘坟墓；咎由自取；自食其果
sign one's own death warrant; dig one's own grave; stew in one's own juice
You're just digging your own grave if you go on smoking so heavily.

自作自受； 自食其果；自寻死路；作法自毙
cut/slit one's (own) throat; have made one's bed and must (or have to) lie in/on it; stew in one's own juice
You've made your bed and you must lie on it.
I would just be cutting my own throat if I stopped work now.

自讨苦吃；自找麻烦
make a rod for one's own back
I've just made a rod for my own back by working for that company, because they always expect one to work many hours without pay.

自高自大；自命不凡
be/get/rise above oneself
Don't be getting far above yourself; you are no more than a secretary.

自断后路；破釜沈舟
burn one's boats/bridges (behind one)
Now we've burned our bridges behind us and we have no option but to go forward with the project.

劣币驱 逐良币
bad money drives out good
"Bad money drives out good" is a proverb and also an economic principle.