1. Take pictures!
Given the availability of digital cameras and cell phones with cameras, there is no excuse for not taking pictures of everything you see. If there is a stain on a part of the carpet, or a mark in the kitchen counter, or a tear in linoleum, take a picture! All marks, existing damage and stains should be photographed for future use. Do the same walk through upon move out. Make sure all preexisting and new damage is photographed. Remember that if you did do damage, this can still help you show that the damage is not as extreme as the landlord may try to imply.
2. Don't be generous to the landlord in the move-in sheet!
The landlord should provide you with a sheet to note any issues that you see. So many people don't make note of items that they believe are normal wear and tear. However, those pre-existing issues may come back to haunt you. If you make certain you list every existing stain in a carpet, worn walking areas, and threadbare corners, the landlord will have a difficult time trying to charge you with carpet replacement at a later time.
3. Be present for the final walk-through!
Do NOT let your landlord do the final walk-through without you. Have your copy of the move-in sheet with you and go room by room with the landlord. The landlord may have been your best friend during your occupancy, but once you move out, that can change in an instant. Don't give them the opportunity to blame you for pre-existing damage.
4. Ask the age of the carpet on move-in.
The most common issue I hear is based upon carpet damage. Carpeting has a "life" span of its own. If the carpet was four years old when you moved in and you lived in the apartment for another three years, it has probably outlived its lifespan. Yet, landlords love to try to charge for carpet replacement. Better the moving tenant pay for it than their own pocket, right?
5. Keep copies of the lease, any addendums, and all paperwork.
Pick a drawer in the kitchen to keep all paperwork in. It will be close by just when you need it. Make sure you review it any time you have a question about whether you are doing something that might be considered breaking the lease. Anything that is not clear should be discussed in writing with the landlord so that you have a record of contact.
6. Make sure all repair requests or modifications are in writing!
If any work needs to be done, request it in writing. Many landlords have "hotlines" for you to call. Go ahead and make the call, but follow it up in writing to the landlord. Even if the writing is an "after the fact" confirmation, you will have records of past issues. This will especially help if there were ongoing issues that the landlord failed to appropriately address during the tenancy and may try to claim against you. Always keep copies of your written requests.