Drive not a second nail till the first is clenched.

The image is of securing one nail firmly before driving another, so the work already begun is not left loose or unfinished.

More broadly, the proverb advises completing or settling one task before taking on the next, especially when the second would distract from finishing the first.

Use it to urge someone to finish an immediate piece of work before starting another. It suits situations where moving ahead too soon could leave the first task incomplete.