Bird of a feather flock together.
物以类聚。
A friend in need a friend indeed.
患难见真交。
One man's meat is another men’s poison.
利于甲者未必利于乙。
An hour in the morning is worth two in the evening.
一日之计在于晨。
One today is worth to tomorrow.
今日事今日毕。/说干就干。