Today I want to show you how you can simply generate an empty world for your minecraft server(We're doing it here with our default world). So go into the server.prosperties and set the following lines:
And if you don't want villages spawning in the air, also set:
But ATTENTION! If you make these changes in the server.prosperties, the settings will get applied for your default world! (In most cases "world").
I hope my short tutorial worked for you. Have fun with it.