Usage of the character 于

mastery of study lies in diligence (idiom). You can only master a subject by assiduous study.
Excellence in work is only possible with diligence.
Practice makes perfect.

gōngzhīyúzhòng

公之于众

[公之於眾]

to make known to the masses (idiom); to publicize widely
to let the world know

dìngyúyīzūn

定于一尊

[定於一尊]

(idiom) to rely on a single authority to determine what is correct
to regard a source (or entity or individual) as the ultimate authority

wújìyúshì

无济于事

[無濟於事]

(idiom) to no avail; of no use

qióngyúyìngfù

穷于应付

[窮於應付]

to struggle to cope (with a situation)
to be at one's wits' end

gōngguòyúqiú

供过于求

[供過於求]

supply exceeds demand

kùnnanzàiyú

困难在于

[困難在於]

the problem is...

shūyúfángfàn

疏于防范

[疏於防範]

to neglect to take precautions
relaxed vigilance

yányúlüjǐ

严于律己

[嚴於律己]

to be strict with oneself

lǎoyúshìgù

老于世故

[老於世故]

experienced in the ways of the world (idiom); worldly-wise
sophisticated

zhēnyúzhìzhì

臻于郅治

[臻於郅治]

to attain a state of perfect governance (idiom)

xiūyúqǐchǐ

羞于启齿

[羞於啟齒]

to be too shy to speak one's mind (idiom)

zhùchēngyúshì

著称于世

[著稱於世]

world-renowned

xuènóngyúshuǐ

血浓于水

[血濃於水]

blood is thicker than water
fig. family ties are closer than social relations

yùjiàoyúlè

寓教于乐

[寓教於樂]

to make learning fun
to combine education and entertainment

yīyúhúdǐ

伊于胡底

[伊於胡底]

where will it stop?

rǎnzhǐyúdǐng

染指于鼎

[染指於鼎]

lit. dip one's finger in the tripod (idiom); fig. to get one's finger in the pie
to get a share of the action

liáoshèngyúwú

聊胜于无

[聊勝於無]

better than nothing (idiom)

jièyúliǎngnán

介于两难

[介於兩難]

to be on the horns of a dilemma (idiom)

jiàhuòyúrén

嫁祸于人

[嫁禍於人]

to pass the misfortune on to sb else (idiom); to blame others
to pass the buck

nányúdēngtiān

难于登天

[難於登天]

harder than climbing to heaven (idiom)

yìyúyánbiǎo

溢于言表

[溢於言表]

to exhibit one's feelings in one's speech

zhēnyúwánshàn

臻于完善

[臻於完善]

to attain perfection (idiom)

xǐxíngyúsè

喜形于色

[喜形於色]

face light up with delight (idiom); to beam with joy

nǐyúbùlún

拟于不伦

[擬於不倫]

to draw an impossible comparison

biǎnduōyúbāo

贬多于褒

[貶多於褒]

to get more criticism than praise

zhòngyú Tài Shān

重于泰山

[重於泰山]

heavier than Mt Tai (idiom); fig. extremely serious matter

Hǎiyúgésōng

海于格松

[海于格松]

Haugesund (city in Rogaland, Norway)

liǎorányúxiōng

了然于胸

[了然於胸]

to be well aware; to understand clearly

píyúbēnmìng

疲于奔命

[疲於奔命]

(idiom) terribly busy
up to one's ears in work

luòyúxiàfēng

落于下风

[落於下風]

to be at a disadvantage

yúguīzhīxǐ

于归之喜

[于歸之喜]

the joy of matrimony (polite phrase referring to a young woman)

nùxíngyúsè

怒形于色

[怒形於色]

to betray anger (idiom); fury written across one's face

jīyúhūwēi

积于忽微

[積於忽微]

to accumulate tiny quantities (idiom)

fánghuànyúwèirán

防患于未然

[防患於未然]

see 防患未然 (fánghuànwèirán)

kēzhèngměngyúhǔ

苛政猛于虎

[苛政猛於虎]

tyrannical government is fiercer than a tiger (idiom)

bìqígōngyúyīyì

毕其功于一役

[畢其功於一役]

to accomplish the whole task at one stroke (idiom)

shēnjiàoshèngyúyánjiào

身教胜于言教

[身教勝於言教]

teaching by example beats explaining in words (idiom)
action speaks louder than words

āimòdàyúxīnsǐ

哀莫大于心死

[哀莫大於心死]

nothing sadder than a withered heart (idiom attributed to Confucius by Zhuangzi 莊子／庄子 ( Zhuāngzǐ))
no greater sorrow than a heart that never rejoices
the worst sorrow is not as bad as an uncaring heart
nothing is more wretched than apathy

shēngmìngzàiyúyùndòng

生命在于运动

[生命在於運動]

life is motion (popular saying with many possible interpretations)
Physical effort is vital for our bodies to function (Aristotle).
Life derives from physical exercise.

shìshíshèngyúxióngbiàn

事实胜于雄辩

[事實勝於雄辯]

facts speak louder than words (idiom)

yīniánzhījìzàiyúchūn

一年之计在于春

[一年之計在於春]

the whole year must be planned for in the spring (idiom)
early planning is the key to success

yīrìzhījìzàiyúchén

一日之计在于晨

[一日之計在於晨]

make your day's plan early in the morning (idiom)
early morning is the golden time of the day

qīngchūyúlán'érshèngyúlán

青出于蓝而胜于蓝

[青出於藍而勝於藍]

lit. the color blue is made out of indigo but is more vivid than indigo (idiom)
fig. the student surpasses the master

yùguǎnlǐyúfúwùzhīzhōng

寓管理于服务之中

[寓管理於服務之中]

to make administration service-oriented

qiānlǐzhīxíng,shǐyúzúxià

千里之行，始于足下

[千里之行，始於足下]

lit. a thousand mile journey begins with the first step
fig. big accomplishments come from an accumulation of little achievements made one by one

qiānlǐzhīdī,huǐyúyǐxué

千里之堤，毁于蚁穴

[千里之堤，毀於蟻穴]

see 千里之堤，潰於蟻穴／千里之堤，溃于蚁穴 (qiānlǐzhīdī,kuìyúyǐxué)

jǐsuǒbùyù,wùshīyúrén

己所不欲，勿施于人

[己所不欲，勿施於人]

What you don't want done to you, don't do to others. (idiom, from the Confucian analects)
Do as you would be done by.
Do not do to others what you would not have them do to you.

shēngyúyōuhuàn,sǐyú'ānlè

生于忧患，死于安乐

[生於憂患，死於安樂]