I made a whole new world for my current fic.
Though it was not that difficult for me, because that new world was based on an already existing world.
Firstly, I made a list of continents (rather say regions to be more specifically) in written data format, without any geographic position info at first. Then I started to think about what cities and/or villages will be in each continents (I only made the ones that will be important to my story, excluding all the unimportant ones that is not even going to feature in my story), and then think about the special locations within those cities such as gyms, market, museums, shrines, etc. (Again, I only made the ones that will be important to my fic)
After these basic information listing, then I started to include other locations that is outside the cities/villages, which includes locations like mountains or hills, lakes and/or rivers, forest and/or plains, etc. And again, I only made the locations that is important to my story, any other places that will not be featured in my fic were not included in my data sheet.
When I had planned my world up to such level, simply a list of geographic informations does not satisfy my enthusiasm, so that is the time I started to draw out the actual map of the world I created, and that is then the first time I actually go think about the actual specific geographic position and/or location of each place. First placed the continents onto the map, then the cities onto each continents, and then the other significant geographic locations, and finally fill in the emptiness in between within unnamed plains and forest.
When the basic map is done, I then started to think this continents seems to be too empty, so I'll add another location to this place, whether it is important to the story or not. This process had performed over and over, again and again until I'm satisfied about the map. Now, the map of my original world is comparable to the scale of current Pokeearth in Serebii.net, and the locations that will be used in my fic were accounted for approximately only 60% of all the locations.
And just another unrelated comment. I think this topic about world-building had already been asked before in the Authors' Cafe for several times in the past.