When I started my PhD in Feb 2014 (gosh that sounds like eons ago), I was introduced to the Pomodoro Technique. It's a time management method developed in the 1980s by Francesco Cirillo. It's just a simple method. It's good for someone like me who have short attention span when it comes to serious work. I seem to have long attention span when playing or wasting time XD.
Anyway, you need a timer with you if you want to use this method. I just use my iPhone. You can download the apps from the App Store if you wish. It's handy. But you don't need an app, really. You can simply use your watch. All you have to do is set your timer to 25 minutes. When the timer begins, you begin doing your work. When the timer beeps at the end of 25 minutes, you stop and take short breaks for 5-10 minutes (not more than that) and do whatever you want like drink coffee, check your messages on your phone or check your emails and such. When the 5-10 minutes break is over, you set your timer back to 25 minutes and begin your work again. Then you repeat doing that many times until you are exhausted or not productive anymore. Then you can stop working and continue your work maybe later after lunch or tomorrow or whatever. You get it right?
So that's Pomodoro Technique. It is believed that mental agility can be improved when using this technique to do your work. So, why don't you try it? Have fun!
Photo take from the world wide web.