One of the biggest challenges a writer will face is creating a believable character. To be believable, the reader has to understand the character's motives, and, if we want an interesting story, those motives are likely to be complex.
Complex motives are what creates interesting characters because these lead to interesting actions.
BUT. . . .
The motives still need to be believable.
Make sure you know why your characters are doing what they're doing, and make sure there's a pattern of behavior.
If Sam is going to steal a car, we need to know she knows how to hotwire a car or where to find the keys. We need to know she's pissed at the car's owner. We need to know that this behavior is exactly in line with who she is.
Little seeds, planted throughout your narrative, bear big fruit.
Okay. That was corny. But you get the point. :D
Be Brilliant!
~Katie~