Do you ever include any of your own moods or events into your story? Everyone has a bad day once in a while. Your character should too. How about a bad hair day? Have you ever had this really annoying song stuck in your head? Or how about some incident - something like a random accident - something like stubbing your toe and now you're limping for a day or two, or cutting your finger and now you're left handed for a while? All of these little things add flavor to your character and helps them come to life without detracting from the overall storyline.
Be careful though, all you want is a little flavor. Though a limp might slow your character down, or having to write left handed might cause some difficulty, these are all things that are plausible and believable. Having a song stuck in your head could be fun to play with. You could have your character singing in the shower or while driving, or even while walking down the street, and then you could stop and cuss yourself out for keeping that annoying song alive a minute longer.
Never be afraid to add moods too. I have, and they too add flavor. It's okay for your character to just get up on the wrong side of the bed once in a while. Maybe he or she didn't get much sleep during the night for whatever reason. Heck, for a girl/woman, it could be PMS - for a boy/man it could be his girlfriend's/wife's PMS. Or how about those days when everything just strikes you as funny.
Your story, whatever it is, is supposed to be life for your character, and like life, we all have random things happen. As you write, things happen to you too. Go ahead and saddle your character with the same thing. Have fun with it. Paying attention to all these little details can be perhaps daunting or tedious, but if you let it, it can also be a release.
Go ahead, let your character step in a hole and twist an ankle. See what kinds of twists your story takes then.