step 1 : plan
To have a good map, you have to know what you're going to do. For large scale maps, it helps to have a sketch, but if your map is smaller, you're probably fine with just a mental model.
step 2 : find the right area to build. If you're building the world from scratch, it takes longer but you get a better area. If you use the default world, you get the world pre-built, but it may not be what you're looking for.
step 3 : storyline
this is completely optional. If you write a storyline, you can invite friends into your world to complete puzzles.
Building
commonly, good maps will have many buildings and structures to work with, but always start with one to see what you think.