just by luck!. rumours tlk abt dirty tricks with yahoo ranking , so far I havent seen nethng concrete workin or me just some gud result but thats abt it. You may want to try drupal, a decent one but for long tail keywords. Else, Keyword density, Site structure, Backlinks, and Aging has worked well for me, good luck!
Maybe things have changed but as far as I know, the only way to get a decent listing in Yahoo is to pay them $299 per year. I don't think Yahoo even lists websites in their search findings that don't pay them. Somebody please correct me if I'm wrong about this.