Sadly, I don't see many tutorials on the 8-bit style, the closest tutorial I know of is devamps of Pokemon from other websites such as deviantART. Like Nintendork said, best thing is to look at the official sprites as reference then continue to sprite and post it, then we can give you critique based on our knowledge of the 8-bit style.
You should sprite some more and post'em! Don't forget you need 4 examples of work to have a qualified sprite thread. Hope you stay around. :P