In my opinion, The thing people overlook the most is taking care of themselves.
We often seek happiness from external things, whether it is a car, significant other, house,etc. The reality is, We have already been given the tools to acquire true happiness and that is from within ourselves. Our hearts beat 24/7, Our immune system is constantly at war fighting off sicknesses and we ignore it all to complain about having something external. Always be thankful and do things you enjoy, not stuff other people want you to do. When you do this you enter a blissful state and attract the same things you wanted before at a much higher rate.
People come and go, Material things come and go or even fade. The only constant thing in your life is you. Eat healthy, learn the power of positive thinking, get into to nature, Life is short and you never know when your time is up so enjoy it.