Auto body repair & detailing: feathering filler, grit sandpaper, sand filler

Question
I have always had a problem feathering the filler material at its edge to get a smooth blending into the undamaged part of the fender, hood, etc.  Can you tell me how to do that?

Thanks a lot!!

Answer
First of you are supposed to grind area wider then your accual body work area so you can feather into steel.  But if you want to cheat. you must sand filler with 80 grit sandpaper.  Then wetsand lightly with 220 wet or dry paper with a block.  
Hope this helps you
     Brian