14 changes to make in your 30s that will set you up for lifelong success

Sam Walton founded Walmart at age 44; Julia Child published her first cookbook at 60. Your best years may be way ahead of you.

It'll depend a lot on how you spend the next decade or so -- i.e. will you start saving or rack up credit-card debt? Wallow in self-pity or learn to be happy with what you have?

Over on Quora, hundreds of people have shared the best ways to spend your 30s in order to lay the foundation for success and fulfillment later on. We sifted through those threads and rounded up 14 compelling responses.

Read on for the small lifestyle tweaks that will pave the way for big life achievements.

1. Stop smoking

If you've started smoking, stop immediately, suggests Quora user Cyndi Perlman Fink.

While you can't undo the damage you may have already incurred from smoking, research suggests that those who quit before age 40 have a 90% lower mortality risk than those who continue.

2. Start going to sleep and waking up at the same time every day

It might be tempting to use the weekends to recoup your sleep debt, but Nan Waldman recommends you hit the hay and wake up around the same time every single day.

If you oversleep for even a few days, experts say you risk resetting your body clock to a different cycle, so you'll start getting tired later in the day. Avoid a lifetime of sleep issues by sticking to bedtime and wake-up routines whenever you can.

3. Start exercising regularly

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"Try to move yourself as much as possible," says Alistair Longman. "It doesn't matter if it's walking, cycling, running, weightlifting, hiking, swimming -- as long as it involves some movement."

In your 30s, you start losing muscle mass, so it's especially important to exercise at this time. But remember to choose physical activities you really love, since you're less likely to continue exercising if you dislike your workouts.

4. Start keeping a journal

"Journal your life! ... Your written records will entertain and endear in your future," writes Mark Crawley.

Even if you'd prefer to keep your musings to yourself, putting your thoughts and feelings on paper can help you deal with stressful events.

5. Start saving money

"Building the habit of saving early means you'll continue it further down the line," says Cliff Gilley.

It might seem like your golden years are a lifetime away, but the earlier you start saving, the more time your money has to accrue interest.

6. Start pursuing a life dream

"Don't delay pursuing your life goals," writes Bill Karwin. "Want to buy a house? Have kids? Write a book? ... Pick one of those life goals and get started. What can you do between now and the end of the year to embark on one of them?"

7. Start learning to be happy with what you have

"If you are content with what you have, you will have a happier life," says Robert Walker.

That's especially true in the relationships domain. "The Gratitude Diaries" author Janice Kaplan found that simply saying "thank you" to her husband breathed new life into their marriage. And psychologists have found that couples who express gratitude toward each other are more likely to stay together.

8. Stop thinking you need to satisfy everyone

"After I reached 30, I stopped feeling the need to please everyone. You can choose your friends and contacts more carefully," says Kevin Teo. In particular, Teo realized he wasn't obligated to be nice to people who were unfriendly toward him.

Whether you decide to whittle down your Facebook friends to a mere 500 or simply hang out more with the people who make you happy, it's important to invest your time and energy wisely.

9. Stop comparing yourself to others

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"If you are unable to do some things in life compared to your siblings and friends, then please be at peace with yourself," advises Mahesh Kaytian. "Don't be harsh on yourself."

Science suggests that comparing yourself to other people -- which isn't so hard to do when your Facebook feed is filled with photos of vacations and engagements -- can be unproductive. That's largely because people can seem a lot happier and less troubled than they really are.

10. Start forgiving yourself for your mistakes

"Forgive yourself your mistakes. We all make plenty of them. Don't dwell on the errors of the past -- learn from them, let them go, and move ahead," writes Liz Palmer in a since-deleted answer.

In "The Happiness Track," Emma Seppala, science director of Stanford's Center for Compassion and Altruism Research and Education, argues that self-compassion is a key component of success. If you're kind to yourself when you fail, you have a chance at learning from your mistakes and doing better next time.

She recommends a simple strategy for exercising self-compassion: Treat yourself as you would treat a colleague or friend who has failed.

11. Start defining your values

Don't let other people define happiness and success for you. Anna Lundberg writes:

"The number one priority at this stage is getting clarity on what your priorities actually are!

"A great way to do this is to define your personal values, getting to a list of your top three is ideal. Then ask yourself if these values are really reflected in your career and your lifestyle today. If not, you can go about setting goals that are aligned with those values, and then creating an action plan to achieve those goals."

You can also take a tip from Stephen Covey, author of the bestseller "The 7 Habits of Highly Effective People," and craft a personal mission statement. It's similar to a company mission statement, except it's just for you.

Covey wrote: "It focuses on what you want to be (character) and to do (contributions and achievements) and on the values or principles upon which being and doing are based."

12. Start reading for an hour a day

Portia Douglass recommends reading for an hour every day. At the end of the year, you'll have spent a total of 15 days with your nose in a book.

If you're looking for some business-related suggestions, we just happen to have 20.

13. Start decluttering

"Living a minimalist life makes everything better," writes Cindy Ah Kioon. "There is more space in your house and this makes it look more visually pleasing ... Cleaning is faster and easier."

If you're looking to start de-cluttering, there's a whole movement to support you, inspired by Marie Kondo's "The Life-Changing Magic of Tidying Up." The process starts with a tidying "marathon," in which you keep only those items that "spark joy" -- and get rid of everything else.

As Business Insider's Erin Brodwin has reported, clutter can be a source of stress for some individuals and families. Then again, people tend to be more creative in messy environments -- so if you aren't feeling motivated to re-organize your entire office space, that's probably okay, too.

14. Stop judging other people

There's another Quora thread where people share the "really small things that tell a lot about a person's psychology and personality."

Behaviors subject to scrutiny include how you treat waitstaff and where you look when you drink out of a cup. Yikes.

But Becki Young advises us to "stop criticizing and judging people." You probably wouldn't feel so great if you were under someone else's microscope.

She writes: "Each of us has our own flaws. Be kind and humble."

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