My guidlines were set by my local luthiers, and they are simple:
1. The best polish is no polish at all. If you must, due to a very dirty guitar, use a polish, use Meguiar's #2 followed by #9. Never, ever, use a polish that has silicones or petroleum distillates in it. Almost ALL commercially sold products do, even when not specifically listed; this includes Martin and Gibson products, as well as most Dunlop products. If you can't determine by the labeling, ask the manufacturer specifically.
2. For the fretboard, use a neutral, genuine fruit/nut oil; never anything with petroleum distallates or silicones. Lemon oil does NOT qualify, as most lemon oils are pretty much petroleum oil based (i.e. distallates) with a lemon scent. I use walnut oil (non polymerizing). Oiling of the fingerboard should be done very rarely, like once a year for a heavily played instrument, for non professional players, once every two years should suffice. Let the oil sit on the wood for about a minute, and wipe off the excess.
Kostas