Maintaining your instrument is beneficial for many reasons, some "advice " online can be highly detrimental to the well being of not only your instrument but , in some cases, even yourself!!
Cleanliness is everything, if the following is followed it will mean a lot less need for costly repairs and remedial work ,and the cost is less than £1 per week per instrument, this is what we suggest if an instrument has been correctly setup in the first instance, this is a service we provide in-house.
Standard electric , change 5 times per year, every 2 months in spring/summer starting at the end March ending at the end of September then every 3 months for the remainder of the year
Acoustic Guitar can be every 3 months.
Bass Guitar every 6 months if possible
These need to be regarded das minimums to minimise fret/fingerboard wear, if changes are more frequent so much the better .
Steven suggested using Crimson fingerboard restorer and cleanser , I wholeheartedly agree with this suggestion for any unsealed boards ,rosewood, ebony etc
For any sealed boards i.e. maple etc WD40 on a J cloth degreases the board and cleans at the same time.
A small amount of WD40 on a J cloth and then buffed off is all that is required for sealed bodies , Nitocellulose and Polyurethane. For natural bodies a light dust over swith a slightly damp lint free cloth is adequate.
Squirt of electronic contact cleaner in pickup switches and jack input periodically is all that is required.
Bridge , squirt of WD40 periodically lubricates grub screws and saddles.
Try and avoid extremes of temperatures and humidity, this again will extend the life of your instrument.
Following the above will not only make your instrument function properly but will make it a much nicer experience when you play it.