2 sentences for 精 (jīng — proficient)

1. 古人云：业精于勤而荒于嬉。

   gǔ​rén yún: yè jīng yú qín ér huāng yú xī.

   The ancients said: 'Excellence in work comes from diligence, while neglect comes from play.'

   Source: Dong Chinese Dictionary

2. 老李的棋艺非常精，在社区里很难遇到对手。

   lǎo Lǐ de qí​yì fēi​cháng jīng, zài shè​qū lǐ hěn nán yù​dào duì​shǒu.

   Old Li's chess skills are superb, and it is hard for him to find a worthy opponent in the neighborhood.

   Source: Dong Chinese Dictionary