I've always made battlemaps for my DnD game so obviously for those the maps are generally story lead and I simply try and keep them interesting with varied terrain. I take from movies, books, pictures, anything that has inspired me and shape them into workable maps.

I've not made anywhere near as many world maps (probably half a dozen to date), but again I always start with a story; what happened in this world that makes it worth drawing? Then I throw down a rough shape (if the shape isn't important) and start adding major terrain and landmarks that are defined by this world history, again looking to the story. As often as not the shape of the continent isn't THAT important in comparison to it's features, but if you know that the southern part of the continent was involved in century long Mage Wars then that area can get pretty interesting If you want your Eastern border to have been invaded by foreign raiders then chances are you want another large landmass that these guys came from. Let the story define where the shape goes and it pretty much draws itself.