unless someone's already mentioned this - don't write in one tone. i've found enough stories on FFN in which characters commit suicide and there's blood and death and cutting and drugs and etc. to make one just as sick as said stories. expand the tones, throw in drama, supernatural, angst, etc.
XD
makes it more fun for others. the gods only know how bored i get finding basically the same oneshot over and over again.
and.....surprises. mustn't forget surprises. and i mean REAL surprises, the ones that'll get readers pissed at you. those are the best kinds, even if you've been the victim of one such surprise.
i.e. kill Sora. the BHK was supposed to die but i decided to hook him up with Kairi, and then hook Riku up with Olette, and then Sora died. no need to talk about all the hatemail and death mail i got afterwards. Mafia included.
dialogue is also a way to give people breathing space. a bunch of huge 'speeches' and elaborate paragraphs kills a potentially good story. have you ever looked at those 'classics' and stare at the massive paragraphs that run on forever and go: wtf?
or how about The Tale of Two Cities and that first sentence that equates a paragraph? yeah. you get the picture. we all need room to breathe.
so add dialogue. good dialogue. banter is also useful for pointing out the smaller details in life. cuz nobody's a hero forever. they're all people, too.
and uh, unless your mary sue isn't a mary sue, don't write one. not recommended. people still do but oftentimes they're predictable. not recommended.
gee...i hope all this hasn't already been said. don't have enough time reading through all 3 pages of posts
^.^"
just from the experiences of a lifelong storyteller. enjoy writing!