Heh, I know nothing. I once tried to learn gimp, but all I learned is that graphics are haaaaard.

Size should be small enough not to break people's reading list, I guess? I know some people get very angry about big images. Looking around, it appears that most of these fic fest banners I see are close to or under 400x400, if that helps.

As for content, uh, not much help with that either. Sorry. Obviously the name of the fest and the year. Maybe there are some Dreamwidth logos/images that would be good? Feel free to do whatever you like, cause I don't know, lol.