Aim to leave the place in better condition than you found it. I sometimes looked for small/cheap jobs I could do around the place every few months, went to the estate agent/landlord and asked permission to do them. It kind of took them by surprise, but they let me do them and it put me very much in the good books with them for if you were a few days late with rent or something. Got a glowing referral from them at the end of the tenancy, which held us in good stead for getting the next place. Competition for tenancies in nice areas or with nice properties can be fierce, and letters of referral like than can be invaluable.
Also, if you are going to be late with the rent, tell them up front and as early as possible so they feel secure.