小心to look out for; to be careful

• 留意每一项细节

  pay attention to every single detail

• 留意关键性问题

  watch out for the key issues

• 弟弟不留意跌了一跤。

  The younger brother wasn't careful and took a tumble.

• 一不留意就要出事。

  You'll have an accident if you're not careful.