I interviewed Sarah J Maas and Leigh Bardugo this summer at Seven Stories in Newcastle and just wanted to take a moment to explain how amazing and inspiring these two women are. Both authors took time to chat with each person who came over to them and offered and posed for pictures. They didn't just sign the books with their signatures and pass them on, but wrote messages and quotes inside, a different thing in each, no matter how many books they had to sign (their poor hands!) and I had A LOT of books! Hardbacks and paperbacks of each author, each different cover, even the ARCs and a poster or two, but they didn't put a limit on how much they'd sign and said they'd sign any and as much as wanted.

Both were so SO lovely to talk to, and very funny! The girl behind me in the queue was nervous as she hadn't any idea what to do or say but came out smiling and talking about how nice they were. My dad came along, wanting to see what all my fuss over these books was about and is now storming through Leigh Bardugo's Shadow and Bone, I think he must've enjoyed himself! I don't think either ever didn't have a smile on their face!

It always so hard for authors to pick favourite characters from their own books, so who is your favourite character from each other's books?

Leigh: Nehemia is my favourite character from Sarah's Throne of Glass series.
Sarah: I'm gonna say Mal, he's so hot. He's so hot! Oh my god, my body temperature actually just got hotter, my pits just got really sweaty.
Leigh: She's so classy!
Sarah: I'm from America! That's how we do things there!

How important and influential is music in your writing?

Sarah: Music literally inspired this entire series for me. Music still inspires every scene, ever character, every moment. Especially movie scores, classical music. I have to have music on when writing or else the silence swallows me whole.

So, do you have different playlists for different moods and different characters?

Sarah: Yeah, I keep really extensive, detailed playlists for all of my books. I have all of my music ordered in order of the scenes in the books, so if anything gets cut or moved I'll take the song out or move it in the playlist, so it helps me when revising to be able to slip into a scene or a mood because I can play the song and get into my characters heads.

Leigh: I never used to listen to music when I was writing, and that really changed when I got into book 2. Now I really use it to get into the right frame of mind. The cool thing is that I've had people make fan-mixes and playlists on Tumblr so I'll go in and if I don't know them I'll take them. Recently, I was driving up the coast to go to a writing retreat, and I was listening to them all, and this one song came on that I'd never heard of and I was like oh my gosh! And I listened to that song when I was writing the Darklings prequel story. So, I've actually discovered a lot of music through readers, which is cool.

So when and how did Winter's Prayer come about, Leigh? ( Leigh's song she wrote for her book series)

Leigh: Oh, gosh! Honestly, it was when I was writing Shadow and Bone, I was driving around in the car and I had this folk melody that my parents used to play stuck in my head. I was stuck in traffic so I just started coming up with words for it. I put my cell phone on voice memo and recorded myself singing the first two verses. They stayed exactly the same all the way through and I just added a third verse. The whole song was recorded in my friend's living room, it sounds like there's a choir in the background but it's actually my friend's wife and her friend. They were singing words from the book.

You have both started a new series, and we've heard many times about the inspirations for your first series' (Sarah: Cinderella with an assassin, and Leigh: walking down a dark corridor at night imaging there's something there), so what inspires these new books?

Sarah: A Court of Thorns and Roses, big surprise, was inspired by music. By actually listening to the Princess Mononoke soundtrack. (A Studio Ghibli film) It's one of my favourite movies ever. A bloody warrior riding a wolf just speaks to my soul. And then I became inspired by Beauty and the Beast and East of the Sun, West of the Moon and the legend of Tamlin. I love fairy tale retellings and mash-ups. It actually wound up going away from those things; it started off as a retelling of the more original fairy tales, but then moved away. Like Throne of Glass has done.

Leigh: I really love rag-tag, band of misfits stories, like Oceans Eleven, The Dirty Dozen and Inglourious Basterds. I wanted to write, basically, a heist story, so that's where the inspiration for The Dregs story came from. And it's exactly that. It's this group of outcasts and misfits from the lowest of the low, this gang, from a slum called The Barrel. They're tasked with an impossible heist that is essentially a suicide mission. If you've read Ruin and Rising you can tell I like friends who are facing impossible odds, so that's basically what I was going for with this. I also wanted to write a cast of semi-despicable characters, which was fun to do.

How important is it for your characters to be flawed?

Sarah: It makes it fun and exciting and unpredictable. The readers have more to relate to. None of us are perfect.
Leigh: I dunno about you, but, I am pretty perfect.
Sarah: You are pretty flawless.
Leigh: It's true. You know it's funny because I've seen criticism levelled at Sarah's work and at my work that could be mirror images of each other. They'll say "Celaena's so vain and cocky!" And then they say, "Alina's so insecure! She's so whiny!" Every time you see someone saying a character's too this or too that, those are the things that make a character. And these are things that guys get away with all the time. I think heroines would be pretty boring if they were perfect all the time.

How important is it for your 'bad' characters to still have good qualities?

Sarah: What was that quote that says something like a good villain sees themselves as the hero of the story? In order to write a good villain, you need to think of them as a person with motivations and backgrounds. I mean like the Darkling, you have hoards of fans that are obsessed with him. I liked the Darkling, I thought he was hot, but he is a really atrocious person, he's a monster! But you made him sexy and approachable; he obviously had something about him that readers connected with.
Leigh: Yeah, I think you should always be able to make your villain's case, otherwise, why would people follow them? The people who live lives that are the most dangerous don't usually come in twirling a moustache rubbing their hands menacingly saying "I'm an evil genius." They're people who are charismatic, charming and appealing, who speak to some part of us that makes us want to follow them, that makes us attracted to them. It was important to me that my heroes not be all good and my villains not be all bad. Sarah actually writes chapters from her villain's point of view, so she's really in their heads!
Sarah: Yeah, that's the witch narrative. I like adding her voice to the story, it was something that I connected with and wanted to add to broaden the world and offer a different glimpse of the two sides of what's happening.
Leigh: We both have pretty despicable kings in our stories so sometimes evil is used as shorthand for really, really, bad. Sometimes people want to be let off the hook, and say "Well is this person good or bad?" "Am I supposed to like Celaena?" It's not one or the other; you're just supposed to be in the story and make your own choices.

Was it always fantasy?

Sarah: Fantasy, sci-fi, I grew up with Star Wars, Lord of the Rings.
Leigh: For me it was always Dune and Labyrinth and Legend. Those were the touchstones for me.

What fictional world would you like to live in?

Leigh: Either the world of JK Rowling or the world of Diana Wynne Jones' Howl's Moving Castle.
Sarah: Yeah, I was thinking of like a Miyazaki film, like Howl's Moving Castle, where everything is beautiful and shiny and you always find a way to save the day.

Finally, do you guys have any advice for YA readers, whether they're aspiring writers or just aspiring to do something with their lives?

Sarah: Don't let anyone shame you for what you read or what you love in general. Many people are gonna tell you not to do xyz things. Do you what you love, and screw the rest.
Leigh: I guess I would just say, there's no expiration date on your talent, so…
Sarah: Aww!
Leigh: Yes, cry! I think there's sometimes the idea that if you don't do something by this date or by this time, that every decision you make is gonna be the end of the road, and its not like that, life's not like that. As long as you have a story to tell, the world will wanna hear it.

• Leigh Bardugo's conclusion to her Grisha trilogy Ruin and Rising and Sarah J Maas's latest Heir of Fire are available at the Guardian bookshop.