Keep your nose to the grindstone
Definition 1 of 1
Pro Tip 1/3Metaphorical Origins
Understand it originally meant laboring in repetitive work, as with a manual grindstone. 
History shows apprentices kept their noses to the grindstone, doing tedious tasks.
Pro Tip 2/3Not Always Literal
It's often used figuratively to convey dedication without actual grinding or noses involved. 
She's in the library with her nose to the grindstone, preparing for the exam.
Pro Tip 3/3Perseverance Implied
Implies steady, continuous effort, similar to running long distances rather than sprinting. 
He kept his nose to the grindstone all summer to save for college.