I joined the Stanford computer graphics lab in 1996 summer after passing the entrance test of porting the light field viewer from SGI to PC. When Pat Hanrahan gave his (last ?) SIGGRAPH talk, I was hiding on stage behind him, doing some live demos while trying not to screw up.
After that, I had no idea what I was supposed to do, so I attempted at least 20 different projects. At some point I almost dropped out to join a certain startup (well if I did I probably could retire by now, but who knows). Fortunately, my advisor, Marc Levoy, was very supportive. Eventually I took courses taught by Robert Gray and David Heeger, whose TSVQ and texture synthesis works inspired me to do a course project. I wrote it up and submitted my first single-authored paper to SIGGRAPH 1999, with scathing reviews, mostly because I did not know how to write yet. I took a writing class, and with the help of my adviser, submitted it again next year which eventually became my first SIGGRAPH paper, in 2000, 4 years after I started my PhD program.
For PhD candidates concerned about not publishing enough in their first, second, or even third year, I hope my experience can help you chill out.
I doubt how many of you could have done worse than I did during the initial period.
Granted, your situation might be different from mine (e.g. some degree program is only 4 years and your adviser might not be as cool as mine), but I want to let you know that your PhD study is likely the only period in your life that you can literally try anything you like without the real consequences of failure. So have fun, and you can learn something from everything you have tried, as I did from these 20+ projects.