Before a specific time with "yiqian"

As well as talking about the past in general, you can use 以前 (yǐqián) to talk about things that happened before a specific time.

吃饭 以前，你洗手了吗？Chī fàn yǐqián, nǐ xǐ shǒu le ma? Before eating, did you wash your hands?
睡觉以前，不要吃东西。 Shuìjiào yǐqián, bù yào chī dōngxi. Before going to sleep, don't eat anything.
两年以前，你认识我老板吗？ Liǎngnián yǐqián, nǐ rènshi wǒ lǎobǎn ma? Two years ago did you know my boss?
星期五 以前，你要做完这些工作。Xīngqī wǔ yǐqián, Nǐ yào zuò wán zhèxie gōngzuò. Before Friday, you need to finish these work.
上大学 以前，你来过上海吗？Shàng dàxué yǐqián, nǐ lái guo shànghǎi ma? Before you went to college,did you come to Shanghai?
结婚以前，你应该先买房子。Jiéhūn yǐqián, nǐ yīnggāi xiān mǎi fángzi. Before getting married, you should first buy the house.

Sources and further reading