If you look at most of the good books you have enjoyed reading (or even at most of the good short stories that have thrilled you), you will find that one thing most good stories have in common is good characters; because of this, you should make sure you are spending enough time around people that you get to know and understand them - and, you should start figuring out what helps you to develop good, believable characters!
As you learn to come up with good characters, and to build your stories around these good characters, another thing you should start looking for is story ideas that are unique and original; when you look at books in the bookstore, you will find that there are a lot of books that have the same general concepts, but what you do not see is that for every one of these books on the shelf, there are thousands of similar books that did not get published. Instead of writing books that are similar to what everyone else is writing - trying to get your work noticed amidst the noise of all the others - this will help you to increase your chances of success (both as far as publication goes, and as far as readership goes), as you come up with ideas that are unique and original.
And along the same lines as trying to develop unique and original story ideas is the fact that you need to be fearless; rather than worrying about failure, be willing to try new things, and keep chasing success until you finally succeed!