One of the things that will catch your eye first is the title of a book, you need to make it short and snappy because you probably don't want it to fill the entire book cover. For example, a book about aliens invading earth wouldn't be called "Some Aliens from Space Do Some Bad Stuff in Space." but it might be called "Attack" or maybe "Escape the Spacemen". A good title sums up what the book is about in only a few words, if it doesn't do that then it should capture the feeling you want people to experience whilst reading your story. Some examples of these are "Charlie and the Chocolate Factory" which is obviously about someone called Charlie and a chocolate factory or "Twilight" which doesn't tell you much about the book but is has a mysterious feel to it and for a book with vampires and werewolves in, fits perfectly.
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