Keep in mind that this storyline and its setting are simply preliminary.
I was envisioning something along the lines of Mass Effect meets Halo and Star Wars.
I'm imagining, if the setting is in a single galaxy, that there is no overarching galactic government, but three major semi-galactic factions, each controlling roughly a third of the known galaxy (the major premise being that there are massive swaths of territory uninhabited and explored).
Unlike Star Wars, I wanted to truly accentuate the idea of scope and scale. So humans will not be the dominant species in the galaxy, though they play a large part. I want it to be seen as though there's always something bigger, stronger, or more dangerous. At the same time, I don't want them to be in the same scenario as Mass Effect, so my premise is this:
When the humans somehow managed to navigate their way to this 'new' galaxy (or perhaps even it is the Milky Way expanded), they stumbled upon an intragalactic war between two or all three of the galactic factions and sided with one, their presence breaking a deadlock or stalemate. This starts the human representatives (or one, a Palpatine-esque figure, perhaps?) to start using this debt as a means to bring galactic decisions closer under human control and power. The government that the humans join (and would later try to control) wouldn't be an evil empire, but how the United States of America is seen now. Some thing it's the best thing ever, others thing it is a modern day hellhole, some say its government is well meaning, others think it's corrupt -- to put proper perspective on the complexity of government as seen through the eyes of its various constituents. It will run the gamut. We'll see genuinely well meaning officials, efficient and effective ones, those who mean well but are hamstrung by the alliances they made to get into power, and outright sinister people.
I have no real idea exactly what my main character will be other than the fact that I want him to defy standards. I do better with morally conflicted or morally bankrupt characters, so I'd imagine he will be Machiavellian. But I don't want to rely on stereotypes and archetypes. For example, he won't be a battle hardened soldier who doesn't enunciate clearly or says "ain't" a lot. He also won't be a hardass who, upon confronting his wife's killer, won't threaten to kill him and eventually have a change of heart and drop the gun. I'd imagine it would be something like (and this is just out of my ass):
Protagonist: You killed my wife. I've spent years hunting your ass down and, finally, I have you literally in the crosshairs.
Wife-Killer: You wouldn't kill me! You're a marine!
Protagonist: Don't bet on it. Finding your wife raped and murdered tends to spin your moral compass.
Wife-Killer: You don't have the balls to pull that trigger.
Protagonist: How clever. This is the best you can do? You're relying on every action flick in history. When the hero confronts the villain and has him at his mercy, the villain gives a ballsy monologue, daring the hero to pull the trigger, and after a few angst-filled minutes, he'll drop the gun and say something self-righteous like 'you're under arrest.' Is that it? I know what you're doing, and it won't work. All you have left is your sorry-ass life. You'd really have me believe that you don't fear death? Heh. I know better. This isn't a movie. And I'm no hero.
*pulls trigger*
Something that defies cliche. I'll try to eliminate character shields and deus ex machinas. If the hero or his sidekick are fighting the equivalent to the Empire's 501st Legion, he or she or they will not be outfighting them with anything short of a panzer or a Star Destroyer. They might get in one punch or one shot before being promptly executed by a combination of superior firepower, training, marksmanship, numbers, and intelligence. If there is a heroine who functions as a diplomat, she will not kick the ass of any trained thug simply because I feel the need to placate the feminists of the world. Unless there is an explanation for superiority, heroes aren't given it simply because they're the heroes and must move on.
So I'm trying to take the advantages of the events of reality and combine them with the fantastical opportunities of science fiction.