When it comes to a book series, we want to switch from copying what we see to never copying what we see. For example, Sue Grafton is famous for her series using the letters of the alphabet in order in the titles, A is for Alibi, B is for Burglar, etc. Even if you were publishing something besides a mystery series, you'd be seriously scorned in the publishing world if you set up another series using this pattern. You're expected to come up with a different concept for your series.
What I can do here, then, to help those of you planning a book series is to cite well-known examples of book series so you can reach for something that hasn't yet been done.
Sue Grafton grabbed the letters of the alphabet, and mystery writer Janet Evanovich took numbers for her wacky Stephanie Plum series: One for the Money, Two for the Dough, Three to Get Deadly, through Lean Mean Thirteen to Takedown Twenty and Top Secret Twenty-One.
How about the days of the week? Yup, they were taken decades ago. Harry Kemelman started his series with Friday the Rabbi Slept Late, then as you might expect, Saturday the Rabbi Went Hungry and Sunday the Rabbi Stayed Home. He eventually ran out of days of the week for his series, but managed to continue it recognizably with The Day the Rabbi Resigned and several others like it.
Don't worry, with the next two examples, you can see that there are actually unlimited possibilities still open for you. Novelist John Sandford has a series centering on detective Lucas Davenport where every title in the series has the word "Prey" in the title: Winter Prey, Silent Prey, Eyes of Prey, and many more. If you picked a different word and built your series around your distinct word, you probably wouldn't be seen as treading on Sandford's toes.
Swedish novelist Stieg Larsson, unfortunately, died after completing just three wonderful books in his series: The Girl With the Dragon Tattoo, The Girl Who Played With Fire, and The Girl Who Kicked the Hornet's Nest. The pattern there is built around "the girl." Again, if you built your series in a similar way around a different word or phrase, it wouldn't necessarily be seen as imitative of Stieg Larsson.
So let's say you're creating a new young adult series around a character who wanted to be a top chef. What would be a non-imitative new pattern to use? Maybe each title has a pun with a different food ingredient in it: Basil Leaves Early. Garlickety Split. Olive Oil Reserves.
Or let's say you're developing a series of language learning books. You could decide to sequence them according to stages of life: Baby Spanish. Toddler Spanish. Schoolkid Spanish. Teen Spanish. Grownup Spanish. Prime of Life Spanish. Gray Hair Spanish.
Ah, the possibilities! Let your imagination go.
In the next and last section of the course, you'll learn how to arrange or rearrange promising elements of a title for best effect.