I've started using my Work Diary to not just keep track of how much I write but everything I do (cleaning, reading, screwing around on the internet). That way in the evening, I can answer the question I ask myself too often: What on earth did I do all day?
Once my entry in my Work Diary was pretty sparse. I frowned and thought of how much money I used to make per day at my job and decided, "Well, this day wasn't worth the money I gave up for it."
I don't think that way very often. Never once have I pined over my lost salary (mostly because there wasn't much to pine over). I have zero guilt about staying home to write, (though I do feel like I have to keep the house clean and the fridge stocked to earn my keep).
However, the thought that my time wasn't worth X amount of dollars changed the way I look at my days.
There are other ways of looking at your days beyond their monetary worth. It can be hard to view your time as limited, especially when you're young, but we don't have forever to waste on dawdling. Was what you did today worth giving up 24 hours of the little time you have left?
I should probably add a caveat, since I've laid on the pressure pretty thick: while it's good to look at your time as precious, feeling guilty over lost time will always - always - drag you down and make you even less productive. Do. Not. Feel. Guilty. Just think about how you can improve in the future and try again tomorrow.