King is rated as a weak if not THE weakest character in the game. Not physically weak, although she IS a skinny girl, but weak in her ability to win matches consistently (it's a game after all). I'm going to try and be as objective about this as I can, but I have an undeniable soft spot for low tier characters. As per usual these characters have to work harder for their wins. That jsut means that YOU have to play better.
King has a very good roll and some special moves that become a great addition to your arsenal if you RC (Roll Cancel) them. For this reason playing her in a groove with a roll would benefit you a lot. King has quite a few CC's (Custom Combos) starters and that makes her somewhat of a threat. Her level 3 supers are of limited use and do relatively low damage. The preference for dashing or running is usually personal and/or situation dependant but running seems to add the most to her game. Lowjumps are almost allways a good thing to have at your disposal. I'm sure she can be played in many grooves at a decent level, as it allways comes back down to the player behind the controls, but considering all the aforementioned things I would recommend playing her in one of theese grooves: A, C or (my favorite) N. K groove being the 4th and slightly more risky choice.