After every practice session, make sure to clean the "belly" (under neath your strings in between the fingerboard and bridge) of your instrument, strings, fingerboard from your instrument as well as the stick (not hair) on your bow.
Excessive rosin buildup can do damage over time and ruin varnish, tear bow hair, and wear out strings.
Always be sure to use a microfiber cloth for the health of your instrument and bow, cotton fibers can damage strings and bow hair.