New brooms sweep clean
New brooms sweep clean.and A new broom sweeps clean.
Prov. Someone who is new in a particular job will do a very good job at first, to prove how competent he or she is. Jill: That new supervisor is awfully strict. Jane: New brooms sweep clean. The new teacher immediately flunked three of the laziest students. "A new broom sweeps clean," one of the students shrugged.