What's the big deal?
OK. You're here, so you've probably bought into the idea that it isn't good enough to fumble under the kitchen sink for the first cleaning product that comes to hand whenever your guitar needs cleaning. Relax though, its not that much more complicated.
Guitar finishes require just a little more care than your average coffee table. A little thought before reaching for the scouring pad and cream and you can have a good looking guitar for years to come.

Lacquer finishes
You'll generally either know you've got a lacquer finish on your guitar (most regular models will) or you'll be able to tell by virtue of the fact that it is (or at least was at one stage) bright and shiny - lacquer finishes are generally buffed to a gloss. Most manufacturers use lacquer as standard. Although Fender have varied the types of finish they use at times, for cleaning purposes the following can be assumed to apply to most of them.

Boring and obvious though it may be, the best advice for cleaning your guitar is to use a slightly dampened (not dripping wet) cloth with no cleaning products on it. With a little effort this will clean most of the grime from your guitar and leave it looking just fine.

I know however, that there are people reading this just dying to get their guitar sparkling and shining and are just itching to use polish. Fine. Go ahead. Just make absolutely sure that the polish contains no silicone. Silicone will do your finish no favours in the long run. It can discolour lacquers and if your guitar ever needs a finish repair or refinish, the presence of silicone will make this a nightmare. Basically silicone and lacquer don't mix. Check the ingredients on the polish you're using as loads of brands contain silicone. If you're in any doubt at all, pop down to your local music store and you'll likely find them selling a guitar polish that will be much safer.

Word of caution: Don't polish your fingerboard.

Danish Oil finishes
I love Danish Oil and use it whenever I can for a finish. It feels great to play on. Couple of things to keep in mind when it comes to cleaning it however.

The good advice about using a damp cloth that was mentioned above comes into play here too. Its the best and safest way of cleaning any guitar finished in Danish Oil. As the finish is generally not as glossy as lacquer, it is not necessary to get that 'sheen' on it.

Its not a great idea to mess around with household polishes on this finish either. What is useful is to occasionally wax the guitar. This is best accomplished with an ordinary liquid furniture wax. I use Rustins Liquid Wax which contains beeswax and carnauba but any beeswax based product should be fine. How often you should do this is difficult to say. Use your common sense - its not necessary to do it every few weeks or anything but maybe once or twice a year. Its not something you want to be doing too regularly anyway as its easiest to do if you strip some of the hardware off the guitar. Certainly remove the strings (and the bridge if its a tunomatic). You don't really want to get the wax caught up in your strings or bridge saddles.

Another word of caution: Don't wax your fingerboard.

The other bits
So what about the rest of the guitar? Hardware, fingerboard and so on. No problem...

Hardware is relatively easy. Most products for cleaning metal, chrome, etc. can be used without any major problems. Its worth checking for silicone in the product and trying to find something that doesn't have it included for your hardware (as much of it will be in contact with the finish - yes, we are that paranoid about silicone). Remember that less is more though - don't clog up your tuners, pickups or bridges with a big splodge of polish. Spray or dab a little onto a cloth and use that.

Fingerboards then... Non-finished fingerboards will love you if you treat them to some Lemon Oil. You can pick up small bottles in your local guitar shop (or on the net if you're stuck). All you need to do is to wipe it onto your fingerboard when you're restringing and leave it for five minutes or so to soak in. You can then wipe off the excess with a dry cloth. This helps clean the board (see below) and helps prevent it drying out.
At this point you can also take the opportunity to clean any fingerboard gunk that has accumulated (usually along the sides of the frets). Use something that won't scratch the fingerboard (a toothpick or similar) and scrape it all off.
On fingerboards that have a finish such as the lacquered maple ones, you should use just a damp cloth. Don't polish them. Its a fact of life that these start to get a bit grubby as the lacquer wears through - live with it.