Well, to be honest, it won't make a change unless you do. The whole 'new year' thing is just a pretext to start from scratch, so jump at the opportunity of outdoing yourself.
What is the key to be in a better state of mind? Only you can figure this out for yourself.
My only advice for you is to discover your hobbies and embrace your talents. One way or another, we have all been gifted - make the most of it.
Let it be your resolution for the new year. And I promise that by the time we reach 2016, you will have achieved more than you ever thought you could. Looking back on the previous months and noticing how far you have come, you will be proud of yourself and all your achievements. Obviously, it will automatically lift up your mood to practice an activity you enjoy doing and excels at.
So what are you waiting for?Find out what makes you happy and start doing it as soon as you can. Good luck, and rendez-vous in 12 months to see who made a change.