Buffing is basically a back and forth motion with the razor that has the razor going over some of the same area repeatedly in a short time span.
j-hook is a motion where the razor head's movement 'draws' a J.
Take a look at Mantic's video on the topic:
For me, the Gillette slide or, alternatively, slanting the razor head ~45 degrees yields good results, especially with milder razors.
Also, I have touble going ATG on the neck - I generally don't. If I do, I perform a pass that's sort of a hybrid between XTG and ATG first, and then go ATG with the razor head slanted using super short motions, usually about half a centimeter, buffed slightly, so that I do maybe 1 step forward, half a step back. With a razor that clamps the blade near the edge, I usually ride the top cap (handle is pretty close to perpendicular to my skin in that case). With a razor that isn't like that (e.g. an EJ/Muhle/Timor head), I often can't do it because of too much blade flex even when riding the cap, but with some of them, riding the comb can work.
I also find that the best prep for me is a half-hour run and a bit of a work out.
One other thing I reckon I should mention - the soap/cream and lather can make a pretty big difference for me. On the neck, I do best with a rich lather that has a nice sheen to it, sometimes a thicker, pre-sheen lather, too.