Secondly, work on marketing. Writing the book is the fun part, but even a great book won't sell if it is left lying in a drawer. Thirdly, keep trying. I once estimated it took me 19,000 sheets of paper to get published. Much of that was just picky-picky revision and reprinting hard copy, but you can't hope to get it right first time.
World building is one of the most difficult aspects for a novice fantasy writer to master.
I think the hard part is creating characters that readers can believe in and identify with. World building is the easy part. It's extremely addictive and much less work than struggling with all those thousands of nasty little words. Creating truly original worlds may be hard, and must be getting harder, but adequate worlds come penny for six. And listening to someone describing his personal fantasy world is worse than hearing about the dream he had last night.