What makes you happy
As a rule of thumb, your happiness will adjust back to anything that is stable and certain like your income, the size of your house, or the quality of your TV. These things do not change day to day so you can expect your happiness level to fade.
On the other hand, infrequent or uncertain positive events, like quality time with friends or an exciting road trip, occur too sporadically to get used to. Inserting more of these hard-to-adapt-to experiences in your life will create longer lasting happiness.