Advice for those trying to write an evolved main character with a book's worth of experience under their belt, though without losing core personality or defining traits
Given that it’s far more common for a genre-fiction hero(ine) to survive into a sequel than their villainous counterpart, there is less emphasis on revamping or replacing a protagonist than there is on evolving what was good into what is now even better. While an evil-doer might become stronger, meaner and more vicious, they will still usually be permitted to retain that one fatal flaw, assuming they are destined to lose. The hero however, will not likely be allowed to get away with the same tricks and tactics they used to triumph the first time – either by their opponent or their readership.
So what is required then, of a second-volume heroic figure? For one, they must show growth in accordance with the ordeals they experienced during the first book. Secondly, they will be expected to go about their upcoming trials in a somewhat new and unique fashion, lest the book be the same old rehashed plot. Finally and despite these first two points, they will ultimately need to remain the same person at their core, unless you’re willing to alter the fundamental nature of the book/series itself.
Whereas it’s perfectly acceptable to begin the first book with a green-as-grass main character whose actions and qualities may be shaped as events unfold, by definition this process leaves you with a matured, defined individual at the time the epilogue roles around. Thus it is that the wealth of knowledge, experience and exposure gained in the first volume must now be taken into account as your hero sets off for their second bout. If you didn’t take notes on everything that he or she said, did, thought and had said/done to them, consider a revisit now, with pen and paper in hand. Every detail, from the fact that he lost an eye in the final fight (and a statement as simple as ‘his eyes scanned the . . .’ can catch you on this) to a comment she made regarding her favourite food, must be minded. Where you once had license to create and choose direction as you went, you now need to read carefully from the map drawn by your own hand.
It goes without saying that a new book means a new challenge for your growing lead character, though while there’s no need to forbid the tactics they used to succeed the first time, their repertoire is now in need of some expansion. If your heroine gunslinger generally resorted to blasting her way out of half the scrapes she got into, consider now dropping her in some form of predicament where such is not a viable option. Recall that while your readers will buy your sequel in order to get more of what they’ve come to enjoy, they’re also expecting more than just the same old shtick. Keep your character doing whatever it is they’ve been doing (it’s obviously been working) but devote a generous amount of time toward showcasing whatever new skills, knowledge or insight they undoubtedly picked up during their first time out.
With all this growth and change taking place, be ever aware of what it is about your character that truly defines them, and ensure that you’re not compromising that core set of traits. If your by-the-book police officer was so scarred by his first-plot experiences that he now tends toward vigilantism, that’s all fine and well, though be clear on the fact that you’re about to take your series in an entirely new direction, and one its readership may not decide to follow. A balance must be struck between changing a hero (and the way they affect the plotline) in accordance with their experiences and morphing them into someone altogether different. If you aren’t looking to transform the story you’re trying to tell, then take great care to ensure that it remains believable for your matured starring role to continue acting as they have thus far.
See also Writing the Sequel -Villains and Writing the Sequel - Plotlines