Inspiration is always there if you seek it and accept it!
For example, I finished No Expectation of Privacy (novel #22 now available) several weeks ago, and rather than waiting while it went out to my first reader and then final read through, I had already begun writing on Milk & Cookies, (novel #23 in progress). Why? The inspiration to continue, continues to flow.
I will admit, that in one sense (an one sense only) it is easier to do this because my novels, though not in an actual series, do consistently contain 'a stable' of characters that have sallied forth throughout the twenty-two, going on, twenty-three novels whose subtitle is: "from the Black Book Investigation of Michael Grant and Associates.
I was always sure, from the genesis of Jamaica Moon (Novel #1), the lives of the characters created in that first novel would continue and I would continue to write their stories. Yes, there would be characters who meet their ignominious or tragic ends, but many characters would appear in book after book with new characters populating each new book. Some new characters might appear only in one book while still others would work their way into 'the stable' and might appear in the next book or other's down the road. [FYI there have been over a thousand characters who have populated these twenty-two books.]
The point is this 'stable' of characters were living their lives, day to day, year after year--having new adventures, new trials and tribulations... just like we do. It was my job as author/transcriber to listen to their stories as they lived them and copy them down, as fast as I could, everything they thought, said and did.
These reappearing characters have grown over the years, as you would expect and no one seems quite ready to retire. If they did, perhaps that would end Black Book Investigation of Michael Grant and Associates... there would be no more from the.
To say I have become comfortable with the escapades of these characters would be an understatement, but never complacent. I have toyed with writing a singularly stand-alone mystery, with totally different characters. But I have not tired of these characters, nor they me... apparently.
However beginning a new novel 'from scratch' without the 'comfort' of listening to the usual suspects, it would be necessary to allow new characters to allow me into their, new-to-me, world and start following their adventures. All that is required is an idea!
The genesis of any story starts with an idea... 1) a character... 2) a place/setting... 3) a conundrum/problem to solve or obstacle to overcome. And when that idea wiggles up from your subconscious to front of mind, those three elements (1,2,3) may appear in any order.. Or you may only be aware of one of those elements and as Harvey Stanbrough would say, "write the first sentence, and then the next and the next".
Trust your subconscious to supply the story as your characters encounter it.
Like I said above: "Inspiration is always there if you seek it and accept it," Whether you are writing your first novel, a stand-alone book with all new characters/places/problems, the process is always the same, let your characters tell their story, "they are the ones living it," Harvey would say.
Start with one of your three elements and start writing, and if you trust yourself, the characters that arrive on the page of your subconscious and then appear on your paper or screen will surprise you and tell their story with all its attendant detail about the 1) place/setting, 2) character/s, and 3) conundrums or problem to solve and obstacles to overcome.
Whether a writer or a reader, your job is singular: BE THE WRITER or BE THE READER. Readers get the chance to be entertained by a story, while a writer gets to be entertained as the characters tell their story and you write it down--in that sense the writer gets to be the actual first reader! To me that is the most fun, as a writer you get to be the first to 'hear' the story.
To all the readers out there, thanks for reading my books.