heck yes peachy, just give it a try. i didn't really know if i could write worth a darn when i started.
missing scenes can be the easiest. just pick a fav eps and watch it, then look for something left unresolved. like two or more of them discussing what happened in solitudes or maybe jack apolpgizing to danny for the other side, or how danny felt after he buried shauri, or sam after jolinar...
maybe sit down, crawl into your fav character's shoes, and jot down a few thoughts from his/her pov.
just pretend you're the charaster, heck that's what the actors do.
now...osiris...i definitely think she should be back. and...here's an evil thought. what if the male body she decides to inhabit is marty's?
yeah, just stay with me here. what if marty comes back as a bad guy (folks have suggested, whispered etc that it would be great)
then either have him in collusion with osiris or have osiris inhabit him (say the tok'ra buried him, someone dug him up and sarced him...) it's sci-fi anything can happen.
it would be fantastic angst potential for both sam and danny...
or...there are those sgc personnel running around on the goauld homeworld from first ones