Cleaning and polishing a guitar is the most basic maintenance task of all, and every player should know how to go about it - but be VERY wary of those proprietory "wonder clean" products, as they could do more harm than good to your instrument.

Your guitar needs to be cleaned regularly to remove the build up of dirt and oils from your hands and the air around you. Make up a simple "cleaning kit" containing the following:-
(a.) plenty of soft, clean rags (old cotton tee-shirts are perfect), but try to avoid those soft, fluffy orange dusters - they leave annoying bits of lint trapped around your strings, frets, and every crevice!
(b.) A decent alcohol based cleaner/degreaser that will evaporate off the surface - methylated spirits is fine, Isopropanol is excellent, lighter fluid will do (be careful!) - but DO NOT use white spirit - it is oil based and will leave an oily residue.
(c.) Guitar polish - look for a decent brand, preferably one endorsed by a guitar manufacturer. You need something containing a wax to protect and shine, but not filled with abrasives that could damage the finish. I've been usung a product called Guitar Care by Terry Gould, which seems to do the job, and I've even used Turtle Wax on a high gloss finish, which worked excellently. I don't think it contains silicones - let me know if I'm wrong!
(d.) Lemon Oil * Use with care!!!* Avoid using this on the BODY of your guitar - it can work its way into and under the finish. I only use it - and VERY sparingly - on Rosewood fingerboards (NOT Maple) after I have given them a good clean with a degreaser, and before I restring the guitar, to stop them drying out and to keep them smooth and shiny. Only use a small amount on a cloth wrapped round your finger; rub it gently into the wood, then leave it to dry for a couple of hours. Wipe off any excess otherwise the oil will build up around your frets and under your strings.

DO NOT USE CLEANERS / POLISHES THAT CONTAIN SILICONE - once it is on, it leaves an awful job to get it off again. Glues, stains, paints and lacquers just will not take to silicone, and - perish the thought - if you ever have to have your guitar repaired, removing the silicone will result in major problems and a large hole in your wallet! Take PARTICULAR care NOT to use household furniture sprays like Pledge and Mr. Sheen - save them for your coffee table....