I was reading a book of Buddhist stories and commentary, Who Ordered This Truckload of Dung? and in it was this suggestion:

When you get up in the morning, smile at the person in the mirror. Your smile will be strained or even something of a rictus. The person in the mirror will smile back.

As a natural reaction, you will return the mirror smile with a genuine one of your own, even laugh out loud. I've done it for three days now, and I have found my spirits lifted and my subsequent day brighter, with a little sense of the ridiculous.

The whole day starts with a smile and a laugh.