Taking care of your instrument is not only the first guitar lesson - it should become a regular habit for beginners and experts alike. Apart from ensuring longer life and consistent sound quality, by this practice you also grow a sense of respect for your guitar, an affinity and a bond with the instrument. You come to "know" your guitar better. On the other hand if you tend to neglect your guitar eventually its quality of sound will suffer. The sound quality is as important as the skill of the player.
You may like to consider using a hard shell case for transporting your guitar. The hard case holds the guitar cushioned securely in place so that the instrument does not get bumps and jerks in handling. This not only protects the body of the guitar, it also keeps the guitar tuned for a longer time.
Many people use soft or cloth "gig bag" which can be zipped up. Although such bags protect the instrument from dust, they do not provide mechanical strength to protect the guitar from possible physical damage. These bags do not even protect the tuning nuts which turn during handling and the guitar gets out of tune. To avoid such problems hard shell case of proper size should be used. The hard cases are designed to take the impact while holding the guitar safely, protecting body and neck of the guitar and keeping it in tune.
Another important accessory is a guitar stand. When you are not playing the guitar you should keep it on a guitar stand. It is not a good practice to lean the guitar against the wall. This can warp the neck of the guitar in due course. The warping will increase the distance between the strings and the fingerboard. This will in turn not only affect the quality of sound, you will need to apply more force to play the instrument. Your level of performance will be affected. To avoid such problems the guitar should be placed on a stand or a level surface. It is good idea to cover the guitar when not using it. You can keep the guitar in its hard shell case when not playing it.
The strings exert considerable force on the guitar. There is enough strength designed in the guitar to withstand this force without deforming. However, if strings are tightened too much, it will give additional strain on the guitar. To prevent over-tightening and also for ease of tuning you can have a tuning device for your guitar. With the help of this device you will be able to tune the guitar quickly and accurately.
If you are very serious about protecting your guitar, you should actually tune down your guitar (loosen the strings) when you are not playing it. You can again tune-in when you decide to play next time. I know it will be a botheration to tune the guitar so many times, but it will provide greater protection.
There are some common sense practices. You need to keep your guitar clean. While you clean your instrument, you can also develop a habit of inspecting the body of your guitar and take action quickly. For example, if any of the strings start rusting they should be replaced.
The movement of the tuning nuts should be smooth. At the earliest signs of any jerky movements, the nuts should be set right by proper maintenance.
Care and maintenance of your instrument is an important guitar lesson which should be religiously followed. The better you take care of your guitar, the better output you can expect.