For many of us, this question can be caused by two different events. In one, we are trucking along and getting the work done and doing a really good job and we want to know what to move to when we have completed a task. This is a way for us to keep the flow do more work while we have the drive. In the other, we are looking for a way out, a way to stop doing whatever it is we are currently doing, hoping the next task will move a little more smoothly or bring more excitement into our lives. We are stagnate and need something else to do thinking it may give us that little spark.
Neither reason behind the question is particularly bad, as we need the spark. When we have it, moving on to what's next is a great use of the energy and drive we have. When we can't seem to find the spark we need, we aren't going to be able to do the work needing to get done. We just have to be aware of the reason behind our question. Constantly searching for, and never finding, the spark should signal to us we need to go about things differently or find something else to do for a while. Without it, we will continue to dread everything that comes next.