Whenever I hand sand with a sanding block, and also often when I use an orbital sander, I keep a stiff bristle brush at hand, and occasionally I scrub off the sandpaper to remove clingy wood dust to re-expose the abrasive particles, before resuming sanding. This little intervention is surprisingly rejuvenating for the sandpaper and allows me to sand more efficiently.
I came up with this idea after I noticed a significant improvement in the work of files and rasps as a result of being brushed and cleaning their clogged-up teeth. What kind of brush to use for sandpaper? I use a natural fiber brush, but a hardware store bought stiff, plastic bristle brush will do just fine. As long as you don’t use a steel brush, you’ll be ok.
This little trick will save you both sandpaper and frustration.