While I know that this doesn't work for everyone, I have found it is the most important part of my day. I am still an introvert and prefer sometimes to be alone, but that makes it all the more important to have valuable one-on-one time to make an impact for others. And part of this is simply selfish in that I can't handle being surrounded by crabby or negative people so I do my best to either improve their attitude, or not be near them.
So, if I want to say that I had a good day by the time night comes, I better seek out people to cheer up. That is how I cheer up too.