this is the way i do it. it is by no means the only way to do it but i get good results with it
I have a neck that needs a little bit of wearing in so it seems the perfect opportunity to show this technique.
here is the neck pre roundover:

its a maple tele neck from warmoth. It has been used a little bit and has a coat of oil on it already. part of the job on this neck is to get the finish a little more consistent and also do some extra fretwork to help give it a worn in feel. that will all be done after the roundover.
I am using an 'irwin' stanley knife blade for this, although i actually prefer a fine razor blade this does the job just fine too!!
here is how i hold the blade - it starts with the first scr@pes at this angle (Blade nearly flat on fretboard face):

and ends at this angle (blade nearly flat on fretboard side):

frets 1 and 2 done

and up to 11:

here is a short vid or me doing a couple of frets
http://www.youtube.com/watch?v=WKy48CP4J9won this neck i am aiming for a consistent roundover so my strokes go in 1 direction only all the way from fret to fret. i do switch directions to even it out but essentially its done in full strokes. If i was doing a relic or wanted it to look old rather than just be comfy i would be doing the strokes back and forth which would give a more scalloped feel to the roundover.
this works great on most woods but if they are grainy (like wenge) i would sand the roundover in
after this a rub with 0000 wire wool will leave it perfectly smooth (probably best to use synthetic wirewool on maple to prevent discolouration)