As you work to plan out your story, consider one thing when it comes to the development of any heroes or heroines. What challenge is worthy of them? What goal is worth their time to achieve? For that matter, what villain is worthy of their talents--such as they might be? What cause could be worth dying for? Answer these questions (if you can) and you'll know more about your "Good Guys" than will fit in to the story you write.
What is worthy of them?
No matter what your favorite genre is, everybody needs something to "push" against that is somehow (in some way) worth their time to "do." Chalk it up to character motivation, if that's how you see it. Otherwise, think of it as the ultimate reason for their existence.
When you get right down to it, there are two major types of hero/heroine. The first can be thought of as "epic." Exceptional people who do really big (i.e., epic) things that are going to save the day, or the world--most of the time. Those valiant souls who selflessly give their life in service to others are martyrs. they are known for their deeds long after their heroic last stand against impossible odds.
The other guys are, well--they're just regular folks who are often forced to do extraordinary things. They don't have big muscles or movie star smiles--but--they do have a lot of heart, conviction, or a strong belief in what they're doing. Somebody has to stop the Bad Guys, if not you--then who?
Hm. Yeah, about that. Epic heroes and heroines have a tendency to know what they want and why they want it. They always seem to know just why those Bad Guys need to be stopped. That's fine and well for them, what should you do when things aren't so obvious? the terrible truth is that some villains are so darned sneaky that nobody knows what they're doing until chaos has hit the fan.
That's why you need to know so much about your Good Guys. Is there some exotic skill or knowledge they have that provides insight in to the problem? Are they just the right people in the right place at the best possible time to defeat those villains? Yes, I know. All that morality and ethics can be heavy, dark, and deep. Why do you think so many heroes/heroines have hang-ups?
The bottom line is this: if you don't know WHY your protagonists win, they won't be believable. You'll have a hard time explaining HOW they are victorious, if you don't know what makes 'em tick. Police officers quite often have a strong sense of right-and-wrong, it's no surprise when they gut it out to find the truth. Secret Agents can have a real "thing" for patriotism that drives them. When all else fails, Mr. or Ms. Nobody might be concerned with the next person your villains harm. That threat may be just enough to bother them in to action.