NEVER use furniture polish. It leaves a wax or waxy residue - IE your instrument becomes a sort of candle with the wood inside the wax. Now find a candle and see how well it resonates when struck or plucked.

Also NEVER use any polish with silicones in - if you have to have any refinishing done it will make it the devil's own job to get the new bit of finish to apply without pinholing.

Guaranteed silicone-free guitar polish is best. A damp cloth (you can use just a smidgeon of soap on the cloth so long as you religiously take it off again with a damper cloth afterwards is OK. Then polish with dry cloth. Bogroll is better than polyroll if you want to use paper, and snotties better still (think how abrasive they can be on your skin).

If you have stubborn greasy marks, real white spirit is usually safe and likely to remove them. Most modern finishes are safe with meths, too - but try it somewhere hidden first, some old finishes are dissolved by meths.

Use metal polish on frets and metal work first, then use guitar polish on the body, back of neck and headstock. Do not use polish on the fingerboard. Use lemon oil (for guitars, not from a lemon) and VERY careful use of a nylon scourer will get the stubborn grease out from round the frets.