I find that if I have to spend time and energy motivating myself then something is "off." Lack of motivation is a sign of some type of mental/emotional block or perhaps an indication that I don't really want to do the task that I supposedly want to motivate myself to do.

In those times and areas where I have long-term, consistent motivation, I am usually motivated by curiosity and a desire to do/be or have something that fits deeply with who I "am" or want to be.