When we talk about bringing a character to life, voice, dialogue, and description all come immediately to mind, but these aren't the only ways to breathe life into the page. And here's where I whip out the old "show, don't tell" phrase that writers either love or hate. It's a little vague when stated just that way, but it's still worth thinking about.
Showing a character in action is not only a great characterization technique, but sometimes it's the only one available. There seems to be a tendency in fiction to have characters that spend way too much time in their own heads. Too much of the "action" is thinking. And while there are people who spent all of their time in their own heads, there are just as many people who don't think a lot, don't speak a lot, and can only be characterized by what they actually do.
So forget inner monologue, improbably conversations, and physical descriptions for a moment. They have their place, but if you focus on them you'll miss out on other techniques. So if you like description, try describing things instead of people. Focus on the character's car, for example. A lot of us is defined by what we own, so you can use objects that are present (or absent) to help give your character more life.
And don't forget to make sure of the reactions of others. In my first novel, Arianna's Tale, I use this extensively with one of my main characters. Damuk is a guy with many different facets, but at first we only see him through Arianna's eyes. As the story unfolds, however, we get to see how others treat him, how they respond to his actions, and we get and entirely different picture. Slowly we realize that he's not actually who Arianna thinks he is, and we learn this because of the behavior of others.
Another great technique is to mislead your readers entirely. Nothing is more fun, as a writer, than playing the role of the totally unreliable narrator. This ploy allows you to give the reader a version of events (and even people) that is either a little off or just totally untrue. And how exactly do you use this technique to reveal character? Typically by the arrival of a character who knows something contrary to the narrative you've set up. And then fun ensues, but this this technique cautiously. As much fun as it is, it can actually annoy your readers if not done right.
A well-developed character transcends genres and makes your book memorable. Use every technique available to you to make sure your characters shine.