duì fúwù chuāngkǒu, mòshēng rén, lǎoshī hé kèhù, yòng 'nín' gèng wěn; duì péngyǒu hé shúxī tóngshì, yòng 'nǐ' yě kěyǐ

对服务窗口、陌生人、老师和客户，用“您”更稳；对朋友和熟悉同事，用“你”也可以。

For service counters, strangers, teachers, and clients, using 'nín' is safer; for friends and close colleagues, using 'nǐ' is also fine.