Living in gratitude and establishing some kind of practice that raises your awareness of that for which you're grateful can do several things.
First, it can keep negative emotions at bay and make you a more positive person. Second, it will make you so much more aware of all the good things in and around you, things that you may easily have overlooked before. Third, it can help you keep a healthy perspective on life—noticing small things that really are large things when you take a broader view. For example, perhaps the person who pours your Starbuck's coffee each morning serves it up with a smile and friendly remark each day. A small thing, perhaps, but how that can brighten a day! Far better than total silence or a snarky comment about the weather or the long lines. When you are positive, you will notice such things ... and appreciate them. You'll feel better, and it will have a ripple effect that'll boomerang back to you, too.
Finally, over the long term you will boost your immune system and add to your health by staying positive and grateful. There's so much to gain. Why not start and end your day in gratitude?