What i look for in an anime / manga is something that can just grab me with the characters persona, and then wrap the story around and say... You better come back next week!
Those i think are the two main things i want, a good story and characters. Though music usually plays a good amount into it as well.
I think... Usually most sports animes drag me into it as well, if it has sports involved or competition... I usually am always drawn to it >_>;;
TL:DR - COMPETITION, MUSIC, CHARACTERS, STORY.