There are a lot of nice resources and ideas for world buiding here but, in my opinion, and as spacemonkey has alluded to, as an author the most important starting point is to understand what type of story you want to tell and begin by creating a world to help you tell that story. The rest are just details to make it feel more real.

For example, if you're doing a future Earth story, you make the changes you want with present Earth to get you to that future place. If you're doing an off-Earth story then you need to ask yourself why you're setting the story off Earth. i.e. What you are gaining by putting it off Earth and what you hope to accomplish with the story. When you know these things, the fundamental physical and social structure of the world almost automatically falls into place. Of course, you can challenge tropes at this point to give it something non-standard, like setting a fantasy quest in an urban centre, but that's your choice. After this it becomes ever greater fine tuning with the addition of things you need such as power structure and economy if you have any kind of population centres, trade or marketplaces; animals and environments if your story has any wilderness; etc.

There are a lot of nice resources and ideas for world building here but, in my opinion, and as spacemonkey has alluded to, as an author the most important starting point is to understand what type of story you want to tell and begin by creating a world to help you tell that story. The rest are just details to make it feel more real.

For example, if you're doing a future Earth story, you make the changes you want with present Earth to get you to that future place. If you're doing an off-Earth story then you need to ask yourself why you're setting the story off Earth. i.e. What you are gaining by putting it off Earth and what you hope to accomplish with the story. When you know these things, the fundamental physical and social structure of the world almost automatically falls into place. Of course, you can challenge tropes at this point to give it something non-standard, like setting a fantasy quest in an urban centre, but that's your choice. After this it becomes ever greater fine tuning with the addition of things you need such as power structure and economy if you have any kind of population centres, trade or marketplaces; animals and environments if your story has any wilderness; etc.