Good question. And for me, just like it does for some of the others, it depends on my overall goal. As an amateur author and artist it really boils down to a few things for me.

Sometimes I have a backstory in mind. Whether it has to do with the culture, a particular event or an overall theme gives me an idea of just how large a scale I am going to be working on. Other times, it has to do with random inspiration. And then there are times that I might just be browsing the many millions of worlds that FTPro can generate (or terrains generated by Terragen) and something happens to catch my eye, just begging for more detail.

When it comes to naming things, I usually don't begin to approach that process until I have an idea behind the culture that will be living in the area. Then my approach tends to follow similar patterns in our own world with the names taking on specific cultural flavors and even spellings (i.e. Lac de SomethingorAnother instead of Lake of SomethingorAnother). And just as Gandwarf said, not everything needs a name. The places that need names are those that will be of interest or play some important role in the grand scheme of things.

GW