The best thing to do is to is to draw up a contract with the current tenant stating that for $X amount per month From DD/MM/YY until DD/MM/YY you are subletting #Y Apartment at XYZ Street, Anytown, USA from the tenant. It should also state that you agree to abide by the lease signed and dated between the landlord and the tenant you're renting from and have a copy attached. You should also get the landlord's permission in writing as the landlord could theoretically not agree to subletting and move to evict you. Don't forget to date the contract. Both parties should have a signed copy. That's about all you can really do as it does not bind the landlord, just the tenant.