I study happiness for a living: 25 'timeless truths' for young people to make life happier, uncomplicated and successful

I've spent 12 years studying happiness and human nature, and in my new book, "Secrets to Adulthood: Simple Truths for Our Complex Lives," I share concrete and manageable advice that solves common problems and gives immediate results.

Over and over, I've been astonished by how a small step can provide a big benefit. Without demanding much time, energy or money, these short rules and timeless truths have made my life happier, successful and uncomplicated:

If you don't know what to do with yourself, go outside or go to sleep.Every to-do list should include one item that can be crossed off in the first five minutes.If you forgot you owned an item, you can probably get rid of it.Sometimes it's easier to make last-minute plans than to plan in advance.One way to answer a difficult question is strategically to misunderstand it.Don't buy things until you need them: Store them at the store.Focus on actions, not outcomes. (Don't try to "learn to play the guitar"; instead, "play the guitar for 20 minutes daily.")Don't wait until you have more free time. You may never have more free time.To fall asleep faster, make sure your feet are warm.If there's something you want to do, make it more convenient; if there's something you want to resist doing, make it less convenient.To get a quick burst of energy, do 10 jumping jacks.Don't let yourself fall into "empty": Keep gas in your car, stash snacks in your bag, charge your phone.Try by age 25: Many lifelong preferences are set by young adulthood, so try new things when you're young.Before accepting an invitation for the future, imagine that you must show up tonight.If possible, have a challenging conversation while walking.Beware of "procrasti-clearing" — cleaning or organizing as an excuse to delay work.To understand a new city or town, visit the local grocery store.Don't do something to make yourself feel better if it just ends up making you feel worse.If you're not sure how to have fun, ask yourself, "What did I do for fun when I was 10 years old?"If you're buying an item that you're not sure you'll use, buy or borrow a cheap one (yoga mat, kitchen knife, tennis racket), and then if you use it regularly, upgrade.Taking advice signals affection or respect: When someone recommends a book, read it; when a person recommends a TV show, watch it.When teaching information or telling a story, highlight what's interesting to the audience, not what's fun for you to discuss.Follow the one-minute rule: If you can do a task in less than one minute, do it without delay.If you can't think of a topic of conversation, ask, "What's keeping you busy these days?"If someone might not remember your name, re-introduce yourself.

Brief and sharp, these little tips distill big ideas into few words; by saying little, they manage to suggest more. I hope you find them as helpful as I have!

Gretchen Rubin is one of today's most influential observers of happiness and human nature. She's the author of many books, including the bestseller "The Happiness Project." Her books have sold more than 3.5 million copies worldwide, in more than 30 languages. She hosts the award-winning podcast Happier with Gretchen Rubin, where she explores practical solutions for living a happier life. Her new book, "Secrets of Adulthood," is out now.

Want to earn some extra money on the side? Take CNBC's new online course How to Start a Side Hustle to learn tips to get started and strategies for success from top side hustle experts. Sign up today and use coupon code EARLYBIRD for an introductory discount of 30% off $97 (+taxes and fees) through April 1, 2025.