Some of you may be feeling as if you simply can't get the character you are creating in your head onto the page. Relax. This is normal for a first draft.
You WILL NOT know your characters until you are at least well past the halfway point or, for most of you, through the end of a complete first draft.
This is because you need to put your characters through their paces.You need to:
Put them in confrontation after confrontation. Afford them plenty of opportunities to lie, cheat and steal and see how they act.
See them at crossroad after crossroad where one path is in their best interest and the other is the right path, or the heroic path, or the unselfish path. In short, the second path is more likely to be the best moral choice.
Until you have put your characters through the first draft of your story you will not only continue to feel like you aren't fleshing them out, but you will feel a little unsure about who they are and what they would do given the chance to cheat on their taxes, cheat on their wife, steal from the boss or give to charity anonymously.
And until you have done this and get much more comfortable with what makes your characters tick, you won't be able to use one of the very best tools available to you to reveal character – interior monologue. You can't know what they'd think until you know what makes them tick.
Just have confidence that if you force yourself and your characters through a difficult (conflict-wise) and focused experience to get something they want, avoid something they fear or eliminate something they must remove from their life, you will gain that intimacy with your characters.
It is this intimacy gained through story experience that will give you the understanding you need in second through fourth drafts where you more precisely use actions, dialogue and interior monologue to reveal character.