It is advisable to keep ALL parts of your guitars as clean as possible - just consider it "routine maintenance".
When you change your strings, dip a cotton bud in some alchohol based - or fast evaporating - cleaning fluid (Isopropyl, or "IPA", is good - Methylated Spirit is good, or even Naptha). Try to avoid anything oil based (such as white spirit), then rub gently along each edge of each fret (that's where the dirt builds up).
When you've done that, you can dip a piece of lint-free cloth (an old tee shirt is useful!) into the spirit and wipe the entire fingerboard and rear of the neck.
Some folks like to then polish the neck and fingerboard with things like Meguiars or Dunlop 65, but in all honesty that is a bit of a labour of love! The maple is very hard, so once you've cleaned it and given it a polish with a clean cloth (I like the microfibre cloths which you can get at any supermarket - the smoother ones, like "Spontex", are the best) you're good to go.
Some folks mistakenly use Lemon Oil on their maple fretboards. It doesn't do it any harm, but you'll only be wiping it on then wiping it all off again!...
