When most people set out to become fitter in the New Year, they're thinking about physical fitness. In fact, getting in better physical shape tops the list of New Year's resolutions. According to a Nielson survey, 37% of people want to stay fit and healthy in the New Year, while 32% of people want to lose weight.

But sadly, most people will never achieve those goals. Statistically speaking, studies find only about 8% of people keep their New Year's resolution.

If more people focused on their mental fitness, however, they'd likely become more successful in achieving any goals they set for themselves--physical fitness or otherwise. After all, your body won't do what your mind doesn't tell it.

Building mental muscle is the key to self-discipline, delayed gratification, grit, and perseverance. And those are the skills you need to become the best physical and mental version of yourself.

Here are 10 New Year's Resolutions that will help you grow mentally stronger next year:

1. I will spend at least 15 minutes a day in quiet reflection.

A few minutes of quiet time gives you an opportunity to reflect on your progress and think about what you want to do better tomorrow. Schedule a few minutes every day to recharge your batteries with a little bit of solitude. It will help you gain clarity and renew your motivation to reach your goals.

2. I will do at least one tough thing every week.

Whether you sign up for a photography class or you join toastmasters, do something that challenges you to step outside your comfort zone. Face your fears head-on can shift the way you see yourself. Rather than assume you need to avoid hard things because you might fail or because you can't tolerate the stress, you'll chip away at your self-limiting beliefs.

3. I'll write in a gratitude journal.

Write down three things you're grateful for every day and you'll change the way you see the world. Studies have linked gratitude to a multitude of benefits, ranging from better sleep to reduced psychological distress. It only takes a few minutes each day, but it's an easy way to boost your mental strength.

4. I'll take better care of my physical health.

Your mind won't operate efficiently if you're not fueling it with sleep, exercise, and healthy food. But, don't make your goal to be thinner or to look good in a bathing suit. Aim for building a healthy body so you can enjoy a healthier, stronger mind.

5. I'm going to develop a kinder inner dialogue.

The conversations you have with yourself impact the way you behave and how you feel. Harsh self-criticism will only hold you back. Commit to talking to yourself the same way you'd speak to a trusted friend and you'll unlock potential you never knew existed.

6. I'm going to become more aware of my feelings.

Aside from happiness or anger, most adults aren't comfortable sharing their feelings. Many people are willing to say, "I've got butterflies in my stomach," or "There was a lump in my throat," because it feels less vulnerable than saying they feel sad or scared. But your emotions play a huge role in every decision you make.

Decide to become better connected to your feelings. Label your emotions and spend time thinking about how those emotions influence the way you think and the way you behave.

7. I'm going to create a timeline for my dream.

A lot of people say, "I'd like to write a book someday," or, "Someday, I'm going to launch my own business." But since 'someday' never appears on the calendar, it's unlikely you'll actually do it. Turn your dream into a goal by creating a realistic timeline for yourself. Even if you can't tackle it for another a year or two, start researching or learning more about your dream now.

8. I'll spend more time with friends and family.

It's easy to get so caught up in the day-to-day grind that you don't set aside time for friends and family. But, studies show spending time with loved ones is critical to your well-being. Make it a priority to spend time with the important people in your life.

9. I'll create a life that is in line with my values.

It's one thing to say you value giving back to the community or you value caring for the environment, living according to those values isn't always so easy. Evaluate where you devote your time and energy and see if you want to make any lifestyle shifts that would help ensure that your life is in line with your values. Living according to your values is an essential component to mastering your mental strength.

10. I'm going to give up one bad habit.

Letting go of a bad habit can help you work smarter, not harder. So rather than saying you're going to eat more vegetables, commit to giving up that bag of chips you eat at lunch every day. Giving up bad habits that rob you of mental strength, like feeling sorry for yourself, will ensure your healthy habits are much more effective.

Build Your Mental Muscle

Don't overwhelm yourself by tackling too many things at once. Start with one change you want to make. You can always start new goals any time of the year.

So maybe you'll decide to start a gratitude journal in January. Then, once you've turned that into a daily habit, commit to going to sleep 30 minutes earlier in February.

Remember, genuine self-improvement isn't about setting a goal on New Year's Eve and then declaring it a success or a failure two weeks later. Mental strength training is about becoming a little better each day throughout the entire year.