To practice, pick a beginning you have already written or write a new beginning to a story that is burning to be written. There are no rules to this beginning at first. Just get it down on paper, or on the computer screen, as the case may be.
Now take this beginning and rewrite it several times. Start by rewriting it in a way that puts your main character in the middle of the action. Make sure this beginning leaves the reader with at least one unanswered question, but it should not be confusing. Action, not confusion. Tweak your beginning several times until you have accomplished this.
Rewrite it again, but this time not with a main character performing an action. Instead, begin your story by focusing on an important thing, place, or animal. Make your beginning full of description. Bring it to life with your words. But also include some type of catalyst. Maybe the location or thing is what springs the story into action. Maybe it's the motivation for your main character. Whatever it is, try to begin the story absent any actual characters. It may not always be a practical way to begin a story, but it's good practice.
Begin the story again, but this time try being funny. Write amusing lines or anecdotes. Have characters amused by everything. Intrigue the reader with all that is funny. Make sure this leads to interest. Keep the reader reading by amusing while at the same time leaving questions unanswered.
Finally, rewrite the story beginning by adding an essay or prologue. Perhaps it's the main character reflecting on what happens in the story before you actually get to telling the story. Perhaps it's the narrator giving information that the reader needs in order to understand the story that will follow. It might just be the history of the setting you're using. It doesn't matter. Begin with exposition. It may sound dreary sometimes, but it can also be helpful..
Look back on the beginnings you've written. They should all be to the same basic story, but they will vary dramatically. Return to these beginnings. Pursue them. See which one takes you further. Perhaps you are now well on your way to writing a novel.
