I usually do everything when I change strings. I use Lemon Oil for treating the Fretboard and it also brings the finish up on the Frets nicely too, but it does dull down again fairly quickly, so bear that in mind.
The trick with Lemon Oil is "Less is More". I apply it, leave it to soak in for a few minutes and then buff the board with whatever you choose to use for the job, old dusters work well.
There was a tremendous product around, don't know if it is still available, called Chrome Fretshttp://www.youtube.com/v/eDa9bUlBIRM&ab