Ok, this is one of the most powerful productivity tips ever: decide on the one thing you are going to do today, and make that decision quickly after waking up!
More specifically, try to think of the 3 to 5 things that annoy you the most / that you have been putting off / that seem difficult to start. There is generally a high correlation between the aforementioned attributes and the importance of the task!
Once this is done, pick one, and only one of these and decide that you will do it today. This will focus your mind on that single task and you will actually find both the energy and clarity of mind needed to get that task started. And as always, once you take the first step, the next one will light up... Only the first 5 minutes are really really tough! (Downright psychological torture in some cases... but the rewards after the first 5 minutes will be enormous too...)