Some people argue that it's a decade solely for you, meant to be spent exploring, having fun, and enjoying being young and alive. Others argue that it is the most defining decade of your adult life and it should be spent heavily investing in your future. If you don't work hard and plan ahead in your twenties, you could be headed down a dark road in your thirties and beyond. However, if all you do is work, you might feel like your youth was wasted.
While hindsight is 20/20, older people love to give twenty-somethings advice. Remember though, most of the typical "twenty-something" advice is based on the mistakes whoever is giving the advice made in their twenties. If someone tells you to just relax and have fun, it's probably because they spent their twenties chained to a drab cubicle while their friends backpacked Europe. If someone tells you to save money and get your act together, they probably took one too many backpacking trips. Take all advice with a grain of salt (and tequila!) of course, and remember it's never too late to completely change your life.