Happiness is determined by what you value in life, whether it is time spent with friends/family, being adventurous, etc....bottom line: be true to yourself and challenge yourself, so you feel good about your accomplishments. If you love animals, find a way to help those in need. If you love people, engage in more social activities.....whatever you choose, just live in the moment and enjoy it. That is how memories are made and what makes life a blessing.
Make sure you have all the fun you can before you die, and do everything you want to do weather it's have kids or whatever, and make sure you don't care what ANYONE thinks, and always know your freaking awesome