Make it lightly.

　　Make light of.

　　Lower one's guard.

　　eg：It's an important job，you must not take it lightly.

　　中英俚语俗语来源：柳宗元·论师道书：“故吾每为文章，未尝敢以轻心掉之。”

　　同义词：毫不在意 To make nothing of.

　　反义词：严阵以待 Poised for action.