It might be a good idea to leave him alone.
让他一个人待着也许是个好主意。
It might be a good idea to take a taxi home in such a rainy day.
在这样一个下雨天坐出租车回家也许是个好主意。
It might be a good idea to take some of the work off his hands.
替他分担一些工作也许是个好主意。