The basic rule is „The apartment must be returned as it was handed over at the beginning of the lease.” The apartment should be kept in good condition during the rental period and should be maintained as if it were your own home. This is also in the lease agreement.
Regular maintenance includes, for example, sufficient ventilation so that no mold can develop as well as avoiding lime deposit build up in the bathroom and toilet. The repair of such damages can be quite expensive.
The furnishings should remain as they are, so no furniture may be taken out of the apartment or other furniture brought in without prior agreement. Do not reprogram electronic devices.