uh... if its a space saga scifi rp thingy it has to have three qualities, though they are fairly obvious ones:
1. It must be set in space.
2. It must have be in a Science Fiction setting. Anything with spacefairing powers, regardless of tech level. For instance Outland was set in space, but still its relativly low tech in comparison to Star Wars. Man uses guns still, all space flight is sub light, it takes place inside the solar system, and Sean Connery is only starting to age.
GM needs to make sure they have figured out which set of sci-fi rules they want to use, and STICK WITH THEM.
Figure out: what kind of FTL travel they're going to use. What kind of weapons are there. Do aliens exist. Where are the aliens. Is humanity a central figure to space politics, and why or why not.
And there must be some kind of conflict that will endanger, at the very least, a planet and by extension, the universe.
Space Operas thrive on the drama between characters, and the tension between the heroes and villains. Characters must be very-much three-dimensional, and the villains must have good, solid reasons for doing what they do. "Expanding the Empire!" is alright, but "I want to destroy the universe!" is tired and cliche.
-SET IN SPACE <33 I totally agree. It's like, the basis of the whole thing xD -COOL TECHNOLOGY I like coming up with wacky inventions or what the future holds :) -AN INTERGALACTIC LOVE STORY You know, like they got parted on two different planets or something :( -WAR/CONFLICT/TROUBLE: Someone got trapped on a planet, sucked into a blackhole, refugees from two warring alien races, intergalactic trouble, planet destroyed, must go on save the world mission :) You get the idea ;] -NONCLICHE RELATIONSHIPS Like, meaningful relationships between the characters, mortal enemies, brotherly love, best friends, etc. You're stuck up there for good (if there's some conflict) so you might as well get along or not get along, you know ? -TEENAGE PRODIGIES ON BOARD Only because I can't play anyone older xD
I can tell you what always bugs me about space sci-fi. That you can find more diversity on a (real) single street than you can find amongst a single alien species that has been traveling the universe for thousands of years. Meet a snooty alien from one end of the universe, you can bet the one on the other end will be exactly the same.