How to Write Your Best Story: Advice for Writers on Spinning an Enchanting Tale by Philip Martin has excellent advice on structuring a story, making memorable main characters and villains, and putting a twist at the end.
One bit that I gleaned from this book is, don't make your characters too likable. That only makes them bland and forgettable. Some of the examples used for memorable characters were Captain Hook, Long John Silver, the Cat in the Hat, Pippi Longstockings, and Sherlock Holmes. Each one has his/her eccentricities. Each is unforgettable once you have spent time with them.
Check this book out for more important story-weaving tips.