Clean things responsibly. Use common sense here, experts say. A thorough vacuuming, sweeping of the floors, washing of the walls and wiping down of counters and cupboards will suffice. In short, leave the apartment in the kind of condition you'd feel comfortable moving into. Don't leave stuff behind.
Many tenants make the mistake of leaving unwanted items such as trash, old furniture or clothing.
If there's a charge to store the items or dispose of them, it can be deducted from your security deposit. If the charges exceed the deposit, the landlord can sue. Get a witness. After you've cleaned, have someone take a walk-through to witness that you did leave the apartment in reasonably good shape. It's best that the witness not be a relative, but it should be someone who'd be willing to testify for you in court.