Ok - When I change strings I do a few things (rhymes...).
Firstly, I clean frets with Planet Waves Fret Polishing System which I get free with packs of strings - Works great, I then clean, remove gunk from fretboard and oil it with Clarinet Bore Oil (Particularly the Leblanc one, my dad's a clarinetist) - Which works superbly, especially if you have harder woods for fretboards, ie Ebony etc.
I then polish the body and back of neck with Dunlop 65 Polish.