Having one's nose to the grindstone

Keep (one's) nose to the grindstone
To work hard and steadily, stay diligent; steadily work hard, without breaks or an uneven pace

• She kept her nose to the grindstone all year and got the exam results she wanted.

Put (one's) nose to the grindstone
To work in earnest.

• The boss told me to put my nose to the grindstone. 
• I've had my nose to the grindstone ever since I started working here.