Calendering and planning is an area that I, like most everyone else, goes though some good times and some not so good times. However, I have found some tools that I like to use to help in planning.
You must first get a better understanding of yourself and how you work and tick. The idea is simple here. The better you understand yourself and how you work, the better you will be able to have more ups than downs when it comes to planning. I would recommend taking a look at Thinktq.