▲common 多用于指物，侧重很常见，不稀奇。如：

It’s a mistake quite common among students. 这是一个学生常犯的错误。

Snow is common in cold countries. 在寒冷的国家里雪是常见的。

▲ordinary 用于物，指十分平淡无奇；用于人，指无特别之处，很一般。如：

His work is quite ordinary. 他的工作很普通。

The inside of the house is rather ordinary. 房子的内部相当平淡无奇。

ordinary people like you and me 你我之类的老百姓

▲usual 指经常看见或经常听到或经常做的事，强调惯常性。如：

We met at the usual place. 我们在往常那个地方见面。

His performance didn’t really come up to his usual high standard. 他没有真正表现出平日的高水平来。

It’s her usual habit to break in with some ideas of her own. 他常常打断别人的话来发表自己的观点。

▲general 语气强于common，侧重大多如此，很少有例外情况。如：

The announcement was met with general rejoicing. 该项宣布受到普遍的欢迎。

There was general agreement at the meeting that the plan was too expensive. 会议上大家普遍认为这项计划耗资过多。

▲average 指相对于某个标准来说属于“普通”的级别，没什么特别之处。如：

It is just an average dictionary. 那只是本普通的词典。

It is about average for the time of year. 对一年中的这个时候来说，降雨量还算普通。