In honour of NaNoWriMo, I thought I would briefly share with you all the top tip I've got for writing aromantic and asexual characters. This is one of the very few times I can give you a "one size fits all" tip and it is this: we're human.
That means that, like any other character you write, we're more than our orientation and we aren't all exactly the same. You don't want to present your aro or ace character as The One True Aro/Ace Experience because it doesn't work that way. It means that you want to avoid narratives that suggest that romantic or sexual attraction are core parts of being human because those imply that we're, you know, not human since we don't feel this attraction.
I know that sounds like a very obvious tip, but honestly it's easily the one I see go wrong the most often because... I don't know, people think that aromanticism and asexuality looks a specific way and if they don't include everything from that way no one will know their character is a-spec?
Let me know if you want me to make this into a series of tips or the like as well as what you'd like to know about writing aro or ace characters!