1.be careful + about/of+ 名词 注意...的
eg.She is careful about/of her food.
=She is careful about/of what she eats.
她很注意饮食。（后面界wh- 从句时，多省略介词）
2.be careful + with + 名词 注意处理...
eg.Be careful with the vase; it's valuable.
那花瓶很贵，要小心处理.
此外，还有be caregul (not)to do/that... 通常与否定的内容连用
eg.Be careful not to be late.
=Be careful (that) you don't be late.
小心不要迟到.
（that从句不使用将来时）