Know your subject when you create fan fiction stories. Be sure to research the topic extensively by watching and reading the series, movies or books. Hardcore fans are sure to notice even the smallest mistake in fan fiction stories that you create.
Write what interests you. If you don't want to read it, then chances are that no one else will want to either. Readers will notice your enthusiasm and passion for the subject matter, lending to a more thrilling read.
Open your fan fiction stories with a hook. Excite your readers and grab their attention within the first few paragraphs to ensure that they continue reading further. If the introduction drags on or bores the reader, he won't bother to read the rest.
Use active voice as much as possible. Passive voice lacks the excitement and power of active text, resulting in words rather then action necessary to keep the reader's interest.
Proofread your work or have someone else do it for you. No one wants to read a story full of misspellings, poor punctuation and lack of proper grammar. Utilize a spellchecker on your computer if available, proofread your own work and ask a friend to read your work. An extra pair of eyes often catches mistakes that one person may miss repeatedly.
Be different. Take the story in directions that it might not otherwise go. Use your imagination and follow your own individual muse to create exciting fan fiction.