Well, I've been writing since I was really young. It started out as awful, kind of self-insert fanfiction, of course, but I was just a kid. At age 12 was when I started working on an original series idea, which I overhauled once I got into high school, and then overhauled once I got into college, where halfway through I realized the entire thing was actually pretty crappy. It'd still come pretty far from where it started, though it definitely wasn't anything with a whole lot of value or sense. The characters were all fairly flat, and while it had some good ideas, it didn't execute them very well. You could tell that it started as something a child wrote.
But I only realized that because a new thing I was working on, which wasn't even fully original and actually took place in an already established universe, had way better characters and concepts going for it than anything else I'd written in my life. It was just for a hobby, too. An online writing roleplay competition where there was no guarantee that I'd even win or get to finish the story. I managed to come in second by a slim margin, but I attribute that to the genuine talent of my final opponent, as well as me procrastinating on the final chapter and finishing it last minute.
Thus, I shelved my old thing that I'd been working on for 7-8 years of my life and started putting more time and energy into this new thing, separating it into its own unique series. And by time and energy I mean I think about this stuff every day of my life, multiple times a day. I'm extremely passionate about it, and if it were to be the only thing I ever got to work on in my life, I'd die a happy man. I don't care for working on other projects nearly as much as this one.
So I've only gotten to where I am through years of practice, failure, reflection, and observation, with many of those years being spent writing not very good material. If I can help anyone else with advice so they have to go through less of that experience, then it's the least I could do.
I've been workshopping a story for several years, part of the reason I haven't actually started writing anything for it beyond concepts is that I have no idea how to start it or what I want the greater meaning to be (beyond some basic in-universe mythology and philosophy). The other part is that I really like building concepts more than actually writing them.
I actually have Angels and Demons in this universe I've been building, but they're just the names of two of the five races in the verse and are basically just normal humans with extra traits.
Nothing wrong with not writing anything beyond concepts. That's most of what my work is. But that's because of my peculiar writing process. I write entirely in my mind, visually, if that makes any sense. I do this while walking around my room and listening to music, which is like the fuel for my inspiration, and by doing this enough times, I gradually rewrite and revise my work until I have it memorized. If I was deaf, I wouldn't be a writer.
The only physically written parts of my work are those that are written by necessity. There's the original stuff from the writing competition, which in total is about 150 Microsoft Word pages, so it's about the length of a novel, though in the grand scheme of things it's only about half a season of the series. Then there's an assortment of short stories I've written for classes over the past couple of years, some of which I'm proud of, and others that I know I could've done better. Lastly, there's the 84-page pilot script I finally finished yesterday. I've been working on this stuff for four years, and I only just yesterday finished writing the beginning of the story. EDIT: Oh, I also wrote a 30-40 page story bible last year, and a miniature one for the pilot this month, so that's important, too.
Though I would recommend at least trying to write out one story arc of your work. I didn't fully come to know my work until I wrote out a huge chunk of it in that writing competition. It might not have ever grown and taken on its current form without that experience.
As I mentioned, I've studied theology, so I often find the application of angels/demons in fiction to be kind of silly. Despite my work being sci-fi, there is actually some spiritual stuff at play, with one major demon character. The story for the writing competition I was in actually had that character's first appearance as the main antagonist, so he was one of the earliest characters I physically wrote. There's a long process with which I created the character based on my studies, and I think the character is really interesting as a result, but it'd take me a while to detail and I think most people would find it weird or boring.
Though I do understand that the pop culture angel/demon tropes are very popular nowadays, so there's nothing wrong with doing it like that, either. The question you have to ask yourself is "What am I doing to make this otherwise common trope unique?" It's not always necessary, as sometimes you don't need to be different for the sake of being different. But it's a good thing to think about, since what's most important is what you as a writer bring to these ideas, even if they aren't entirely novel. Vampires are another common example, as they've been adapted in so many different stories, but often the authors will change them in unique ways that make them interesting and stand out from other works.
For example, one of the foremost characters in my work (and protagonist of that writing competition) is a character heavily inspired by HUNK from Resident Evil. However, I took inspiration from some other influences as well, along with reworking the core of the character into something of my own imagination, resulting in a kind of character I don't think has really been done before, the way I've executed it. So while the HUNK influence is still present, it's only one element, and it's only temporary, until the character grows later in the story.
Noice or a 
Noice?
