Many fantasy stories are accompanied by a map. Think about Tolkien-his stories ranged in many different places, and he always had a map to accompany them. Think about the Inheritance Series (Eragon, Eldest, Brisngr), it has a map of the places where the story takes place. The Door Within, The White Lion Chronicles. There are many more as well.
I'm not going to try to convince you of the importance of a map, they are very handy for the reader and the writer though. I'm going to attempt to explain how to draw a convincing map. I'll do my best, even though I'm not the best artist or geographist lol.
Below are pictures of a map that I had worked on for the book I was writing before the one I'm working on now.
To make a fantasy map realistic though it needs to feel realistic. I had a good laugh this morning about how unrealistic my first attempts at maps were.
In a real world, or more importantly in a real map, there are many rivers. That's something I've noticed. Plus, the world is mostly water. To make it feel realistic you need to have many rivers. But not too much, you've got to find a balance.
Also, a river isn't completely straight. It will curve and swerve through the map until it reaches the sea or it's stopping point. It will also branch out numerous times. I have a map that has about seven or eight rivers that came from two rivers.
Another thing is mountains. In a fantasy world there are-or should be-many mountains and so in your map there should be many mountains. Because it's a fantasy world though it's the writers decision on how long the mountain range is, how many there are, etc. It's good to have a variety. Going back to the example with Tolkien, he had a mountain singled off. It was even the major place in his first published work, The Hobbit. So it's good to have a variety of mountain ranges. Mountains can also be used as border points, to separate lands. Just off the top of my head I can think of a possible story making a huge mountain range that is so tall and fierce-some that no one dared cross them.
Then comes forests-it is relatively the same as mountains. You want to have a good variety of sizes of forests and there should be many of them. They can also be used to hide ancient secrets such as the Seven Sleepers in Wayne Thomas Batson's Rise of the Wyrm Lord.
When making borders to the oceans and sea keep in mind things such as gulfs, cliffs and havens.
Since it is fantasy you have an advantage-you can throw in things such as gigantic cracks and chasms in the ground, trees that reach past eyesight into the sky, rivers that flow so fast that if you were to go in you'd be swept away and be unable to get out. Don't be afraid to really go into things that are impossible-it's fantasy. But still be realistic enough that you don't lose the reader.
Also don't feel limited when you draw maps. It's usually a good idea to not put bounds on your world so that you can always explore new lands. That's part for the fun of the writer though.
And last but not least, do not feel like you have to be an artist to draw a map, I can barely draw but it doesn't stop me from at least trying to draw a map, however horrible I may be.