Examples
qǐng请nǐ你shì xiān事先bǎ把jì huà计划gào su告诉wǒ我。
请你事先把计划告诉我。
Please let me know the schedule beforehand.
事先打个招呼，别叫我临时抓瞎。
Let me know beforehand instead of catching me on the hop at the last minute.
除非他们事先修好刹车，我才会买车子。
I'll only buy the car if they fix the brakes first.