Expressing simultaneous actions with "yimian"

一面 (yìmiàn) is a more formal than 一边, but is used in the same way to express two simultaneous actions. It is used in the following way:

Structure

一面 + Verb + 一面 + Verb

他喜欢一面吃东西，一面看电影。Tā xǐhuān yīmiàn chī dōngxī, yīmiàn kàn diànyǐng.He likes to eat and watch movies at the same time.
我告诉你多少次了，别一面躺在床上一面吃零食！弄得床上都是碎屑!Wǒ gàosù nǐ duōshǎo cì le, bié yīmiàn tǎng zài chuángshàng yīmiàn chī língshí! Nòng dé chuángshàng dōu shì suì xiè!I told you so many times, don't eat while laying on the bed. The "clean" bed now has crumbs all over it!
他们一家人一面赏月一面吃月饼。Tāmen yījiā rén yīmiàn shǎng yuè yīmiàn chī yuèbǐng.They enjoy the moon and eat moon cakes together as a family.
你会一面拍头一面揉肚子吗？Nǐ huì yīmiàn pāi tóu yīmiàn róu dùzi ma?Can you pat your head and rub your belly at the same time?

一面 cannot be shortened in the way while 一边 can:

一面 can also be used to express two aspects of a situation, which are not necessarily being enacted simultaneously. This is the same as the structure: "一方面...一方面..." or the English "on the one hand...one the other hand"

政府一面要控制通货膨胀，一面也要保证一定的经济增长速度。Zhèngfǔ yīmiàn yào kòngzhì tōnghuò péngzhàng, yīmiàn yě yào bǎozhèng yīdìng de jīngjì zēngzhǎng sùdù.On one hand, the government is going to control inflation, but on the other hand, it's definitely going to protect economic growth.