The reason I say that you don't need anyone to tell you how to be happy is because the 21 things on this list are very, very obvious. Having said that, it's very helpful to be reminded once in a while. Each item on the list will make you think: "duh, I knew that."
The thing is, we thwart our own happiness even though the path to get there is straightforward and something we already "know" deep down.
If you have to do just one thing today, how about "Don't judge." This will be triply effective because it covers 3 topics on the list:
14: Mind Their Own BusinessWhy self confidence you ask? Well, the less you judge others, the less you worry about others judging you. Think about the people in your life and whether or not this holds true. It certainly does for the people I know...
16: Love Unconditionally
20: Self Confidence