Writers are often faced with the dilemma of whether or not to write a series. Do they want to create a character that keeps coming back book after book, or would they rather focus on a new character for each story?
Seeing the same character time and again can actually be a benefit for both the writer and the reader. For the writer, it’s nice to already be familiar with a character, knowing his likes and dislikes, how he would behave in most situations. Plus, the writer has the opportunity to develop the character from book to book. In the first book, the character could start out as an immature brat and develop into a mature woman, or perhaps a close-minded man learns from a variety of experiences and becomes less judgmental. Anything is possible. As for the reader, there’s something comforting about picking up a book and already knowing all the main people in the story. It’s akin to getting reacquainted with old friends.
That’s not to say writing about the same character in multiple books is easy. Probably the hardest aspect is keeping the person and all the repeating secondary characters interesting enough that readers want to go on another adventure with them. If the characters remain static, they can become tiresome, even dull. Nobody wants that.
One way for the protagonist to change is through their personal relationships, particularly the romantic ones. In a new series, the first book is often where the main character meets the new guy who will later be her partner. Sometimes she goes on a first date with him, sometimes the relationship starts off more acrimonious, and they don’t make it to the first date until Book Two.
If the protagonist is an amateur sleuth with a day job, she can also make progress in her professional world, starting as a store clerk and ultimately becoming the shop’s owner or getting hired as a fledgling newspaper reporter only to become the editor as the series progresses.
The key to a series is keeping the plots and characters fresh while still holding onto those traits that readers love. With any luck, the series will continue for years, and the readers will be right there waiting for the next book.