A dissertation is a marathon, not a sprint. Keep a portfolio of tasks at different difficulty levels so you can always find something to finish each day. Those small wins keep you moving forward.
First of all, remember, a dissertation is not a sprint. It's a marathon. So some days you're going to be more productive than others. Have a bunch of tasks you're going to do. Don't have just one. And leave some simple, easy ones always out there so you can get those accomplished. Because getting something accomplished helps you move forward every day.
