Cleaning
Lacquer and Most Modern Guitar Finishes

I have a huge assortment of cleaners in my arsenal and my preference depends on the condition and type of finish. The easiest way for a consumer to be safe is to use the cleaners made specifically for instrument care and/or recommended by the manufacturer.

This Martin was cleaned using a spray polish and flannel cloth.
Because this finish is quite thin, porous and has some fine finish cracks a paste cleaner would have left an ugly white residue in it's pores.

1948 Martin D-18

Though difficult to tell from the picture, this older D-18 was really dirty. If you look at the bass side, top corner you will see my initial starting point. On instruments such as this with decades of dirt and grime a good clean up can be quite time consuming. This is not what I would call a "courtesy cleaning" as it is a real workout.

Sprays are good for cleaning gloss finishes and relatively clean instruments, these are non-abrasive and can be used frequently. If your instrument has a satin finish you will want to avoid using a cream polish and sprays are far less abrasive.

Polishing Clothes

While a nice flannel cloth is more then adequate for 99% of players, those trying to polish dark, show all finishes will find that a high quality Micro Fiber towel/cloth is a little better choice as they are softer and add less swirl marks.*
*Swirl mark - an extremely fine scratch usually only detected when looking at the finish from 14 different angles under light with magnification invented by the devil to drive detailing freaks crazy! hehe
 

Paste Cleaners and Polishes

Paste cleaners which do not contain abrasives or silicon are good for cleaning up tougher dirt and scuffs on gloss finishes.
There are plenty of good brands and products out there. Matter of fact, many of us use/used Meguiars® and other car polishes to clean instruments long before they began marketing instrument polishes. Most products that are safe for clear coat automotive finishes are safe for lacquer guitar finishes as well.

WARNINGS:
Cracks and Scratches Bear in mind that liquid paste cleaners will quickly contaminate open cracks and fill nicks in the finish. If your instrument has an open crack or scratches which penetrate to the wood I do not advise using a paste on the finish (or at least not on that area).
Contaminating an open crack with polish will make repair more difficult and when scratches or heavy wear expose bare wood it is often filled with the polish which leaves it white.
When I feel as though a paste/cream polish is absolutely necessary for polishing an instrument that has lots of wear and tear I may rub the cleaner deeply into my polishing cloth to reduce the chances of filling the crack with polish.


Vintage Finishes Vintage instruments often have very thin finishes. Some will be varnish instead of lacquer and require gentle care. When dealing with a vintage instrument it is best to have a professional advise you on cleaning it.
View other instrument care products.

Cleaning the Fingerboard and Frets

Unpainted Fingerboards When the fingerboard is not painted I normally use 000/0000 steel wool to clean it. Most Ebony and Rosewood fingerboards do not have finish on them, though there are a few exceptions (Rickenbacker's come to mind). Extra fine steel wool can remove crude from the fingerboard and shine the frets as well. Naphtha is also helpful with certain kinds of crude.
Make sure to cover or mask over pickups on electric guitars when using steel wool so the pickups are not covered with the steel wool 'hair' that is shed when cleaning.

Painted Fingerboards  On a fingerboard that is painted (nearly all maple fingerboards) you should refrain from using steel wool. Most of these I will clean the same way I do the finish, but fingerboards with missing finish or wear spots must be treated differently. Boards that have a satin finish will require the same precautions as stated above.

Oil Oiling an unfinished fingerboard makes the board look good and may help to prevent dryness which can lead to cracks.   While there are many oils safe for fingerboards some may leave a sticky residue which attracts dirt. Mineral oil, danish oil and lemon oil are all popular choices.

Polishing Frets - If you've seen my fret work (or at least some pictures of it) then you know I like smooth shiny frets. That's not simply because they look pretty...their highly polished crown makes for some slick string bending. The fact is, steel wooling one of my fret jobs would actually introduce more scratches because I use much finer abrasives to polish newly crowned frets. However in the real world where an instrument has been played, using steel wool to polish the frets is satisfactory. If you have a maple or painted fingerboard you will have to protect the finish.

Satin Finishes

Care of satin or flat finished instruments is a little different from that of a glossy lacquer finish. Using a paste polish or compound on a satin finish will change the sheen eventually leading to a glossier look. If you read the cleaning recommendations of the manufacturer you will find that many simply recommend a lightly damp cloth.

Sanding, polishing or buffing a satin finish can change it's texture and/or sheen.
Have you noticed a shiny spot where your arm rests? Repeated contact and rubbing can provide the necessary polishing to turn satin finishes glossy...a natural occurrence and to be expected. Though the areas can be "scuffed" to dull the shine created by the friction I would avoid doing that repeatedly on thinner finishes.
 
Did you know?? Most cleaners should be used on finished surfaces only. Read the bottle for instructions and precautions. Applying a paste cleaner to the bridge or fingerboard (raw wood) will leave white residue behind in the pores. Yuck.

Article: Caring For Your Instrument (Low Humidity & Other Dangers)