Time mangement

Never seems like there is enough time to get everything done I'd like too. So how do you pick what things to do and which things to put off. I've started reading a book called "Getting Things Done" better known as GTD. It's been helpful but I'm just getting into it. I've also picked up a book for a Java Class, speaking of which starts in 30 min. So for me I think I pick jobs/projects I'm confident I can tackle quickly and put off the projects where there is not clarity. Perhaps I should put getting clarity as a project?.. hum.. maybe. I'll have to come back to this thought/topic.