A few tips:
Don't do it alone. Reflection can be a conversation. Talk it out with your spouse, your best friend, your dog. Someone you can trust who gets you talking out loud (which is different than ruminating alone, spinning your wheels). Choose someone who has a different view of the world than you. Or a different flavor of personality. Just make sure that person won't criticize you into the ground.
Don't do it online. Take a break from media, from the phone and tablet and laptop. Go low tech on this one. Grab a pencil and paper and write your thoughts out. Or try meditation to calm the nerves.
Don't be too harsh. I hear so many people berate themselves for not starting sooner, or not achieving X, Y, Z by a certain point. The end of the year doesn't have to be about tallying achievements. Go deeper.
Identify how you solve problems. Warning: it involves emotions. What emotion are you feeling? When have you felt like this before? Was it when you were trying to find that first job? Were you trying to figure out your major in college? How did you figure it out? What strengths did you naturally tap into?
I've been trained as a writer, so I can journal my way out of a lot of problems, but maybe you're visual. Can you Pinterest your way out of the problem (okay, I know I said to stay offline, but this could be an exception)? Can you cobble together a picture of what you want instead of your current career life?
How can you get more autonomy and feel more skilled in your career? Research shows those two things can make a worker feel satisfied. Can you take a class, ask for a month off for a rewarding trip, gather a pile of books that will take you in a new direction?
Just some questions for the end of the year. Happy holidays, and here's to a wonderful 2014!