keep (your) nose to the grindstone

to continue to work very hard, without stopping.

I've only got six weeks before my exams start so I'm trying to keep my nose to the grindstone.

• not be worth the paper it's written on
• not be worth the paper they're printed on
• not be worth the paper they're written on
• not be your bag
• not be your brother's keeper
• not break the bank
• not breathe a word
• not budge an inch
• not by a long shot
• not by any stretch
• not by any stretch of the imagination
• not care a fig
• not care a hoot
• not care a toss
• not care tuppence
• notch below
• notch below someone
• notch below something
• not come up to scratch
• not cup of tea
• not cut it
• not cut the mustard
• not day
• not do any favors
• not do any favours