Sometimes we loose our determination and energy when we are making art. Production slows down and we spend a great deal of time looking at the unfinished work and pondering the next step. We loose the direction in which we thought we were "going" with a piece. In general we get lost.
Try the technique alla prima or something similar. Alla Prima is an art term used for art that is created in one sitting. In Italian it means 'at once' or 'at first attempt'. Much of the traditional alla prima painting was working into wet oil paint or wet on wet. The colours would blend and muddy and create a certain look that was a little less precise.
Give yourself a particular amount of time to create your alla prima work - a fews hours, a day depending on scale, material or whatever constraints you are working with.
Ensure that you won't have any distractions during that time. Cell phones off. Reduce stimulation like sound. Try to eat food in advance and have water handy - reducing the distraction of breaks as much as possible.
Set up your space, choose and lay out a limited range of materials to work with - brushes, paint or whatever your medium of choice may be.
Work. Work with focus and unwavering attention. Keep working until you reach a point were the work could be finished - now you get to take a moment to consider if the work is complete or if you should continue on.