I do laugh preparation exercises. First work on my muscle memory. Many years ago I learned that in order to play my mandolin, I had to practice the same thing over and over and then my finger muscles would remember how to do it without me even thinking. I am training my face muscles to smile all the time. There are 300 muscles in your face and they all can learn to have a smile with practice. Their natural state is not relaxed, it is what your have taught them to do. Why not teach them to smile. What happens then is amazing. People see you smileing and their natural response is to smile back. Note Dali Lama; he smiles all the time and most people can not help smileing back. Also, when ever I see myself in a mirror or a window and I am smileing, I cheer right up. It is contageous. The second thing I do to prepare for laughing is I listen carefully for what others say that is funny. I mostly ignore the negative and focus on the funny. This is a good exercise in listening and I hear a lot more funny things. As soon as I hear something funny, I laugh, out loud. I laugh so the person that said the funny thing hears, so others hear and listen more carefully and also so I hear myself laugh. This builds my confidence, gets me in a good mood and exercises my already strong smileing muscles even more. It also helps others to enjoy a good laugh.