Sometimes we wake up and we already know if it's going to be a good day or a bad day. Sometimes these determinants are extremely small things. Sometimes they are larger things, like falling down several flights of stairs.
The best way to have the best day is to forget about those things and pretend that each new day is a clean slate. Don't approach the day as if it will be wonderful, because something could go wrong, and then you are disappointing yourself even more. And if you go into the day thinking it's going to be horrible, you might miss out on the things that are great about the day.
Think of each day as a blank canvas. Leave all of your previous ideas and extraneous thoughts at the door and start anew. It will help you to clear your mind and focus on getting the best out of the day ahead of you.