Technique? Kinda' Wrap the sandpaper around something flat (scrap piece of wood) to ensure you are presenting a clean, flat surface to the pad.

I actually use a mill bastard file, rather than sandpaper, but that's personal preference.

It's not so much a matter of 'roughing up' the pads (trying to get money out of them ) as it is deglazing them--removing any oxidized surface that has coated the smoother, stickier rubber with time, use, or non-use.

Be sure to inspect for, and remove, tiny shards of metal or other debris while you're in there.

Further, clean your rims' braking surfaces with a rag and some isopropyl alcohol.

If all else fails, wear an iPod and get back to riding