When it comes to fantasy I begin with the very basic outline of the story, A being the start B being the finish. Once that's been established I move onto the first ladder of world building - the world. I then select the appropriate location of the story, this gives me climate, tectonic movement, length of daylight. Then I evolve the story way beyond its basic A and B routes into, in summary, something much greater. Then I place the geological elements I need into the map, mountains, forests, rivers. Then I select locations for cities and towns based both of what I believe to be appropriate locations for these things (defense, resources, transport, trade) while also mutating it if the story requires it, but I will bend the story slightly to make the world its told in fit. Once I've got my starting points for the story chosen, the geography decided, the lands drawn out, I hit the play button in my head. Anything in life has a sensitive dependance on initial events. So long as my characters have a persona decided, I know the choices they make, the places they visit. Every now and then during this play through I will fill in elements of the world, culture for example. If these changes effect the story anywhere else I rewind and play from there, always updating the world as its fleshed out more. Eventually one the entire world is complete the story, based of geography and the persona of the characters there really is only a few ways the story can go, and I let it play its self out for the most part.
You don't have to make up the world all at once. I'd write the story, write scenes that take place in certain places in your world, and then fill in the gaps later.
Creating a world of your own for a fantasy novel is a mammoth task and I would say that the main rule is that you have to really love and believe in your world for it to be successful. Creating the world is the most difficult and longest aspect of writing a fantasy novel for me as you not only have create the basic structure but you also have to pinpoint finer details that many readers will probably not even notice. Also, you must ensure that you are completely familiar with your world as you write as it is very easy to make contradictions, especially if you take a break from your writing, which I once did. Coming back to it after a few months, I discovered that i had forgotten many details about my world and it took me a while to get back into the right frame of mind. Rule for making a successful world in terms of the reader? Good, vivid imagery is possibly the most obvious and patronising thing to suggest but I have read some worlds that I just can't picture in my mind. Making a world is taking on a big challenge but it can be very satisfying when done right. I must also echo what other readers say: don't try and create your entire world at once. You will need to bend your own world's rules to fit with your plot sometimes. At second edit, I am still making new discoveries about my fantasy world. And also still discovering gaping holes in it!
