One of the things that impressed me most from reading fantasy fiction was how the authors created entire worlds that provided a rich history full of legends and tales as a backdrop to their stories. When telling a tale filled with fanciful creations and situations, having a background is absolutely essential. For me, it is a natural requirement for the characters in the stories to come alive, and for the entire story to have that believable quality that draws the reader into the world as if they were one of the character's companions.
For the Rangers of Laerean series, I started out with map making software to create a continent for my new world. As I was doing this, I considered the entirety of the planet as a whole, though that would not really be something seen within the stories themselves. For instance, I considered the planet to be much like earth in size and proximity to the sun and moon, and in the tilt of it's axis. This allowed me to create a simple calendar for tracking time in the stories. I decided to simplify the calendar, so there are no leap years or odd days in each month, etc. A simple 30 days per month, and 12 months per year.
I did add one little quirk. The tilt of the axis and orbit around the sun would create an anomaly every 69 years, in which the northern hemisphere of the planet would undergo a colder than normal winter, called a Dread Winter. This is actually essential to future books about the world. The Dread Winter will play an important role in future stories and in the development of the history. That is for a future tale, however, so I am not going to elaborate on that just yet.
I named the continent Hir and began to place symbols on the map to indicate landscape features. The continent itself is quite large, so the northern areas would be a cooler climate than the southern areas. I then placed Major and Minor cities, as it would be beneficial for readers to see these locations on a map, rather than try to visualize it all from the stories themselves. I did not specify exact locations for villages, towns and homesteads or other similar communities. Nor did I indicate exact road positions on the map. I did not feel these were necessary, at least not at the beginning.
Finally, I began adding details using the Ranger Archives, to provide more background information about history, races, economies, politics and such. The whole process has left me with a backdrop of rich lore and history to draw upon and to provide life in the stories I have begun to write. As time progresses, I can easily add more if needed, including new continents if desired. This is the process I used to create the Lands of Hir for the Rangers of Laerean series.