i guess whta u want to say is 一言一行
言 in chinese means language ,and the words u said.
行means action and the behavior.
一 means one , in this case we should translate it into every.
so this sentence means every words somebody said and every behavior somebady did.
let's make an instance,
在国外,你要注意你的一言一行,因为此时你代表的是一个国家的形象。
when u r in a foreign country,u should watch your every word u said and every behavior u did,because u are representing your whole nationailty.