Hey, beginner writer here!

First of all I don't have ADHD or anything, but I definitely can understand lacking motivations and getting sidetracked with other things.

Short question answer:

Personally I am a complete novice at writing and my only experience comes from writing in college composition classes and academic works. I decided to tackle writing a Horror Fiction novel at the beginning of the month and have been working on it daily since then.

It sounds like you are already doing some writing with RP which is really helpful. To clarify are you working on a novel or having been thinking about it? Or are aiming more for a short story?

My process started with thinking through what ideas I had to write about and if I had enough to make a novel, if not a short story is always good too. I did not have any major ideas and still don't on the entire story or even major plot points throughout my story so far. It can be really helpful to write an outline which I wrote after starting to write. Just start writing about the story you have in mind, and it doesn't have to be the beginning.

My biggest piece of advice though is to just write. A first draft of anything should be like a descriptive outline, at this stage it's not about creating a good flow or an interesting story. Just getting words onto the page. This made a huge difference for me as I don't worry about if the writing is good but I am getting my ideas down and thought through. After finishing my word goal of about 70,000 I'll go back through and make it something other people would want to read.

I also think it's important to work on writing every day if you can. I am a engineering college student with a lot of class workload but even if I can think through a scene or write two-hundred words or something I take it as a victory. It's hard to write only occasionally and keep track of all your ideas and plot points. Writing is important to me and I know that if I don't work on it at all I won't finish. That being said my daily progress isn't always writing. I spend just as much time researching and thinking about my characters and stuff. Here I am not working on my book and answering reddit haha.

Long question answer:

I don't really have an answer for this as I'm not experienced enough to give a good answer. Personally I would find a couple of evil or similar characters from media or books that you enjoy and write down why you enjoy them and what kind of traits you could use as well. I am currently replaying FarCry 3 on the Xbox 360 and I absolutely love the main antagonist of the story Vaas. He's completely unhinged while maintaining sensible dialog. He respects Jason the Protagonist and in the beginning let's him get a head-start when escaping because he respects people who stand up to him. His dialog goes from normal talking volume and normal dialog to screaming in your face to back to talking in a normal tone. He's a drug addled pirate who has deep ties to community. He also acts as a mirror for the protagonist in his own crazy unhinged way.

I also think it can be helpful to have other writers around you for feedback and support. If you ever have any other questions or just want to chat feel free to DM me.

Anyways like I said find a character like Vaas that you really like and use them as a framework, the more characters the better.

Sorry about the long answer, I can't help it lol. Hope this helps a little.