I have preached on praise.  I enjoy praising.  Like many others, it is often difficult to praise when things are not great.  Simply, situations and circumstances can affect our praise.  This is sad, but I think it is human nature.  It takes discipline and a will to praise when the storm clouds seem to hover over us, but there is a song that I love to listen to when I am facing trials in my life.  The video is below and I hope it blesses you as it does me...