plain and simple, should I create an idea for one book and continue, or should I create my own fantasy world and from that make a story from the world which I have created?
Write one book at a time, you will need to create your world for one book anyway. It's up to you whether you make your world first and build a story from it, or if you have a story in mind and build a world around it, either works. But focus on one book now, use all your best ideas (don't worry you'll think of more!) and make it awesome.
QFT. What's the point of planning a series? What happens when you get to the end of one book and decide you don't want to work on it anymore? You've wasted time planning something you find you don't like. Work on something to begin with that'll help you flesh out your world and setting, then go from there.
A series comes about when you get a world stuck in your head that you love so much, you can't help but go back there. Remember it's equally good/ fun to finish one story and decide it's time to create another world.
Create the world and then you can make as many stories in it as you'd like. I mean if it's a fantasy you have to have a world in mind anyway.
Personally, I create the world first and let the stories come over time. But hey, it's different for everybody. The downside to the world-building approach is that you run the risk of getting trapped in your own world encouraging all kinds of terrible writers-block and cliché. That being said, just try to let it flow. Write a bit. Build a bit. Rinse and repeat. - AR
