buckle down

Idiom: "(to) buckle down"

Definition:

to start working seriously

Examples:

1) After getting all C’s his freshman year, Dave buckled down and got straight A’s the next semester.

2) We need to buckle down and get started.  We have to finish this by the end of the month.

中文解释：http://www.youzienglish.com/main/idiom_of_the_day/to_buckle_down/cn/