Depends on the whole purgatory thing being true or not and whether or not it sheds any light on how easy it is to get into heaven. Sure you won't go to heaven but you also won't go to hell.
Now, excluding all the purgatory/afterlife crap, I'd do like Light did, except only to the worst of criminals, I'd also do political assassinations and wouldn't touch police and the like. I would also make it a priority to never respond to challenges like Light did. I'd burn the names I've written after they died as well just in case. I'd also vary how they die a lot. If this shit happened people would think it was an act of god... but I'm an atheist and that wouldn't sit well with me, so I'd have to kill off the pope and other religious leaders.
I'd use the deathnote to make those I kill send me money :D