Yeah, i'd say take study on sidewalk - it's much easier to figure things out  what goes where and what follows what. I'm not much of methodologist - just quick edit for your sprite - changed proportion a little, added two more frames if you have a room for it, perhaps - 4 frame is a funny walk as it is=),  adjusted leg spacing and twick a few pixels to point far and close parts.=)



 Hope it'll help. I recall someone posted a  tut for iso walk, just can't remember who.