For me, character development has always been about personality, motivation and history. If you have none of these your character is a cardboard cutout; if you have all three, they're practically a protagonist.
The blond officer marched into the operations theatre and saluted crisply. "Lieutenant Hans Zimmer, ready for orders, sir!" Colonel Anders looked up from his maps. "Come in, Lieutenant," he said. "The news from Berlin is grim. I need you to carry out a desperate mission."
Personality is crucial. When we meet people we often like to pigeon-hole them into categories - he's brave, she's nice, they're creepy. As we get to know them better we start to consider them as having several different traits that come out at different times. Characters in a story are much the same; you want to introduce them with one trait, then gradually revealing a more complex personality to the reader. Consider the difference between a confident general and an aggressive one. Both could be excellent generals, but already there is a real difference in their styles. If the character sticks around for a while, I add another one, and eventually a third. What if I added conservative to one but shy to the other? How could you resolve someone who was aggressive but shy at the same time? This gives them a layered, complex personality that can begin to seem very real. I use a list of 20 traits and pick up to three for each character - that gives me over 1,000 unique personalities to work with.
The cocky blond officer marched into the operations theatre and saluted crisply. "Lieutenant Hans Zimmer, ready for orders, sir!" The twinkle in his eyes and the grin on his face marred an otherwise parade-perfect performance. Colonel Anders glanced up in irritation. "Come in, Lieutenant," he said harshly, then went back to studying the maps in front of him. "The news from Berlin is grim. I need you to carry out a desperate mission."
Motivation is the second key to character development. Very few people in the world are obsessed - most have any number of goals, some of which are unrealistic, some of which may conflict with others. Again, trying to introduce them all at once will overwhelm readers, so you start off by showing one, then gradually reveal more layers to your main characters. When I introduce a character I try to come up with what they value most. General A may be serving his country out of a sense of duty, while General B could be in it for the money. Both could be capable men who were always loyal - but they would have different reactions to the same event. I enjoy giving a few characters conflicting goals - this can make them seem flawed and human. Once again, I use a list of 20 broad goals and pick up to three, so again, over 1,000 unique combinations.
The cocky blond officer marched into the operations theatre and saluted crisply. "Lieutenant Hans Zimmer, ready for orders, sir!" The twinkle in his eyes and the grin on his face marred an otherwise parade-perfect performance, but he didn't seem to care. Colonel Anders glanced up at the young man and tried not to wince: his uniform was covered in mud, but his gold braids were carefully cleaned. "Come in, Lieutenant," he sighed, as he went back to studying the maps on the table. "I don't have the time for this, but it's time to begin your education as a man. We're losing the war, son." His voice caught and Anders cursed himself for showing weakness. "I need you to carry out a desperate mission."
History is the final step in making a character seem real. You may have just come up with them ten seconds ago, but if you write as if that is the case your readers will sense it too! Having a past makes them seem far more real. Consider the difference between walking in and seeing an old friend or walking in and introducing yourself; the tone of the story changes and becomes more natural, less formal. You can still share the same information without needing to spell it out for the reader - showing, not telling. I don't have any list I use for this - I just try to come up with something. History can be tied into motivations and personality easily - perhaps the money-loving general isn't greedy but needs the money to keep his wife in the style she's accustomed to - or he's being blackmailed by his gay lover. Perhaps he became greedy in the first place because he used to be an aristocrat - before all noble titles became so much worthless paper. History could even be as simple as the recognition of a shared experience or mutual aquaintance.
The cocky blond officer marched into the operations theatre and saluted crisply. "Lieutenant Hans Zimmer, ready for orders, sir!" The twinkle in his eyes and the grin on his face marred an otherwise parade-perfect performance, but he didn't seem to care. Colonel Anders rose from his maps with a roar. "Lieutenant Zimmer? God! If only your father could see you now, Hans!" The two men embraced fiercely. "Ach, if only the news from Berlin were as good..." His throat caught for a moment. "We're losing the war, lad." The young officer stared at him in dismay. "It's true. And that's why I called you here tonight - to see if a Zimmer can't pull the Prussian fat out of the fire once again..."