It doesn't mean you never think about the past nor fantasize about the future. To some extent, these are healthy things to do, but life happens in the present, and this is where you need to invest most of your energies.

So, for example, next time you are having a conversation with someone, block everything else out of your mind and give that person your undivided attention. Then notice how much more enjoyable your interactions with others become. Like everything else in life, seizing (and living in) the moment is a habit that takes practice to master. Start today!

Embrace the differences

Science says that, on average, humans are 99.5% genetically similar to one another. If that's the case, then it must be the 0.5% that makes life interesting. Or can you imagine a world without differences, where we are all the same? How boring would that be?

If you agree with this, then why would you ever live your life in constant comparison to someone else's? The beauty is in our differences--what sets us apart from everyone else. Embrace those differences--from personal interests to career goals--and brace yourself for how much better your life will be when you do so.

Establish true friendships

Friends are people you love and respect and whose company you enjoy, not benchmarks of success for you to measure your life against. If you are constantly comparing yourself to someone, then that person is not a friend but rather a competitor. Comparison is the nature of competition, not friendship. Competition is great for businesses and free markets, not for personal friendships.

Tune out the background noise

In today's interconnected, high-tech world, where we are continuously bombarded by advertisements for material things or ideas about how to live our lives, it's hard to keep yourself centered and focused on what really matters. What really matters is whatever you decide is important in your life--not what an advertiser wants you to believe.

There are many ways to tune out all this unnecessary noise from your life. Watch less TV, for example. Spend less time on social media. Meditate. Immerse yourself in a new hobby. Anything that requires you to disconnect from everyday life helps.

Focus on what you have, not what you're missing

Mastering the art of contentment is perhaps the single most important thing you can do to live a happy life. Contentment does not mean having no goals or life ambitions; it means that you are happy with what you have at every stage in your life.

Happiness does not have conditions. In other words, never say, "I'll be happy when..." Be happy now, with what you have and don't have now. If you can't be happy with what you have now, you will never be happy with what you think is missing in your life for you to achieve happiness.

Keep it simple

Last but certainly not least, keep it simple. Keep your life simple. A simple life is not an uninteresting life; it's just a life without unnecessary baggage to hold you down, keeping you from doing the things you really want to do.

If contentment is the key to happiness, simplicity is the lock--both equally important to opening the metaphorical door to a happy life.