白手起家；从头做起
from scratch; start (again) from scratch
He's a successful entrepreneur who started from scratch.

 
白纸黑字
in black and white
I don't want to hear you promise to pay me. I want your promise in black and white.

 
本末倒置
put/set the cart before the horse
You're putting the cart before the horse by buying all this furniture before you've got the house.

本性难移
a leopard never changes its spots; a leopard cannot change its spots
It's not surprising that he was sentenced to five years in prison again, because a leopard never changes its spots.

生龙活虎；生气勃勃
alive and kicking
My father is 82 years old but he is still very much alive and kicking.

生杀大权
the power/right of life and/or death
The ancient kings of this country held the power of life and death over all their servants.

功败垂成；功亏一篑
(there's many) a slip twixt (the) cup and (the) lip; pipped at the post
I have to tell you that your plan is a slip twixt the cup and the lip.
We thought the owner would agree to sell us the house but we were pipped at the post by a more generous offer from someone else.

附注：1. twixt 或 betwixt 是 "between" 的旧式拼法。2. 在赛马中，一匹马快到终点时突然被另一匹马超越称之为 "pipped"；现今，无论在任何比赛、竞争或选举中，只要在最后关头或最后一刻被击败或被超越时就可使用这成语来形容，如例句所言，眼看要成交时，有人却出更高的价钱把房子买走了。

左右为难；进退两难
on the horns of a dilemma
I was on the horns of a dilemma when I was offered another job because I still had/felt a great deal of loyalty to my boss.

左右逢源
butter both sides of one's bread
She's buttering both sides of her bread -- she works for our company during the day and has another job during the evening.

四面八方
on every hand; on all hands; in all directions
On every hand was a charming view of rocky buttresses and wooded heights.

打铁趁热
make hay while the sun shines
John may as well make hay while the sun shines, because he is young and healthy and able to earn a lot of money.

半途而废
fall by the wayside; wither on the vine
How's that book you were working on?
-- Oh, I'm afraid it's fallen by the wayside.
My wife who was trying to lose weight had already withered on the vine by eating cream cakes.


失之东隅，收之桑榆 (即得失相当；损益相抵)
What you lose on the swings you gain on the roundabouts (常缩写为 "swings and roundabouts")
It's a bit of a swings-and-roundabouts situation. (a swings-and-roundabouts situation：得失相当的情况)

未雨绸缪；以备不时之需
for a rainy day
You'd better save some money for a rainy day.

出人头地；功成名就
make one's/its mark
After having been working for the company for more than 15 years, he finally made his mark.

以升容斗；以小容大；做明知办不到的事
put a quart into a pint pot (通常用于否定句)
Many new people have moved into this small town and they have nowhere to live. You can't put a quart into a pint pot.

以怨报德；恩将仇报
bite the hand that feeds one
The man had worked for the company for several years. When he was caught stealing, his employer felt that he had bitten the hand that fed him.

以眼还眼，以牙还牙
an eye for an eye (and a tooth for a tooth)
I didn't believe in the death penalty -- an eye for an eye -- but how else can we stop this sort of thing?

以其人之道还治其人之身
pay someone back in their own coin
II decided to pay her back in her own coin and refuse to help her.