Buying an expensive guitar is the end of a process, it's the beginning. You have to take good care of your guitar to ensure that you get consistent sound for an extended period of time. You just cannot use the guitar without getting its dirty, especially oil and fingerprints from your hands. If you use a routine of doing a little cleaning every day you will avoid a lot of possible problems in future. Here are some simple steps to keep your guitar neat and clean even after long hours of performance or practice.
On ships the engineering department has people known as wipers. That's their job - wiping up oil. Unless you want to hire a wiper you will have to learn to do the job yourself because that's the key to maintaining the good condition of your guitar over the years.
A soft cotton rag is the exact thing you should use for polishing and cleaning your guitar. If you want to get fancy you can use a special guitar polishing cloth. These clothes are made of flannel and are available in most music stores. They are not only for guitars; these specialized wipes can be used to clean any musical instrument.
I keep a small pile of old cotton T-shirts that have been discolored for many sessions of washing. Do not throw old T-shirts away; they make a perfect guitar cleaner and guitar wiping tool as many washings have left them virtually free from lint. Also, by using old cotton clothes you do not have any risk of making scratches on the polish of your guitar.
Try and avoid T-shirts that have lettering or logos since they may create scratch marks on a delicate finish. For the same reason, never wipe the guitars with paper towels, especially if your guitar has a lacquer or shellac finish.
Also remember to turn the cloth frequently when wiping up the oils from the surface of the instrument. Rock stars are not noted for their laundry skills, but if the instrument is smeared with lot of oily fingerprints, repeated use of the same piece of cloth will only add to the haze, so for Pete's sake wash your wiping cloth every once in a while.
Each time you wipe your guitar, you actually perform a polishing job and if you maintain this as a lifelong habit you will be giving your guitar a longer life. Don't avoid cleaning places like the area under the strings just because they are difficult to reach. Extend the corner of your cloth under the strings to ensure that the surface does not gather dust.
Make sure to polish the strings carefully after each playing. Take each string individually with piece of your cloth and rub it along its entire length. This maintains the tonal life of the strings for a longer stretch of time. Some professional guitar players are even of the opinion that you should wipe the strings a number of times during a performance.
If you have persistent oily marks or smudges you can try the same technique people use on their eyeglasses; by slowly "huffing" on the area to add a little moisture and then wiping again.
There are also commercial cleaning solutions that come in three main types; oil-based, water-based and water-based mixed with light abrasives. If you don't want to use commercial cleaners you can simply use a good furniture polish on the wood and liquid dishwashing detergent mixed with water for the hardware. It should be sprayed on the cloth and not on the surface of the instrument.
It's best to establish good habits early for the daily care of your guitar and if you follow these guidelines you should have no problems with your guitar. But sometimes the instrument acquires some marks as well as scratches or damage which is beyond simple cleaning. In that case you may have to take your guitar to a professional to get it back to the original finish.