Il faut balayer devant sa porte

Literally: One must sweep in front of one's own door

Example: “Il critique la gestion des autres services, mais il ferait mieux de balayer devant sa porte.” — He criticizes how other departments are run, but he'd do better to sweep before his own door.

Origin: Everyone keeps the doorstep in front of their own house clean before complaining about the neighbor's. German uses the same broom: jeder kehre vor seiner eigenen Tür.