Examine your nubuck leather piece before you start to work to determine where the piece would naturally get more wear. This is usually around the edges -- anywhere it would come into regular contact with people sitting, and be worn by friction or darkened by skin oils over time -- the front edges of seats, head- and armrests, and the edges of pillows.
Gently rub the nubuck with a fine-grit sandpaper sponge in areas that would receive the most wear.
Rub edges with a rough chunk of rock or coarse sandpaper for more focused wear, being careful not to go through the leather -- you probably want to avoid the ultra-distressed route of patches or Frankenstein-like stitching on your nubuck item.
Spritz your absorbent nubuck piece with water and rubbing alcohol, cold tea or a leather conditioning lotion. Leather conditioning products leave nubuck leather looking darker than their original color with a slightly slicker texture.
Scratch the surface of your nubuck furniture or accessory with your fingernails for lighter scratches, or the dull edge of a key for deeper gouges. Take care not to rip the leather.
Brush your nubuck item all over when you're just about satisfied with your distressing job. Smoothing the nubuck with a brush, as the manufacturer did when it was originally processed can blend the different distressed areas for a more natural look.