well i've actually judged some stuff before so I basically look for:
1.Difficulty of run (spin both ways, change up the tricks, technical rail tricks, etc.)
2.cleanliness (basically style, how good the tricks look)
3.overall impression (Flow of run)
and I leave a little room for creativity or something that really sticks out (in a good way)
hand drags and falls are no bueno, but finish your run if you can.