Hopefully, over the last few weeks, I've given you a lot to think about in crafting characters. That wasn't by any means an exhaustive list, nor was it meant to say that those elements can never, ever be used. Like with many things, your mileage may vary. Some people don't mind those elements; even I find them tolerable if a given story makes up for it in other ways or if it seems like a passing mention rather than something the story relies on heavily to drive plot.
I mostly focused on what not to do or how to fix tropes and stereotypes that can do harm when understood outside the context of the bisexual community. I'd like to offer a bit about what I like to see in bi characters. Please note, this is only what I like. Others have different opinions on the matter, and what I say should not be taken as a statement for an entire vast community of people with many views.
In no particular order, this is what I like:
1. Characters who are well-rounded and fully fleshed out. I cringe less at tropes and stereotypes when they are part of the larger personality of a main character. It's the flatness of a character which makes the bad portrayal more evident.
2. Characters for whom being bi is just a facet of their lives. I don't really feel like I need a character to have multiple relationships within a story to "prove" their orientation. It's a lot like real life. Of course, some throw-away line isn't good either, but there are ways to do it where that isn't necessary. Just know your character and that person's life story. Readers may never see it, but the better you know your characters, the better we will, too.
3. Growing into bisexual orientation. I admit, I avoid coming out stories like the plague. They can be incredibly tropey, and I think they're overdone. That said, when done well, they can be really good, and they can be affirming for many people. We see lots and lots of gay and lesbian coming out stories, especially in young adult fiction. It would be great to see more bi stories! This is also a good way to explore adult coming out, since many people identify in some other way before discovering themselves to be bisexual. A great way to knock the "bi until gay" trope on its ear is to have a "gay until bi" character. It's realistic, after all.
4. Non-monogamous relationships that aren't threesomes. Not that I mind a threesome in a story (if done well), but there are so many other options. While it's not good to assume every bi person wants an open relationship or multiple partners, it is realistic to our community that many people do. I'd like to see that honored in a non-tropey/sexual fantasy way.
5. Characters actually identifying as bisexual. Sometimes, it's not any more necessary than it is for a character to repeatedly remind us they are gay/lesbian. It can be distracting and unnecessary to the plot. However, we do often get shoved in the "no label needed" category. We have a saying: "anything but bi." It's incredibly frustrating to read over and over again characters discovering gay or lesbian identities and actually using the words, while bisexual people avoid the word like they're going to get struck by lightning for saying it (or any other multisexual orientation, such as pan or omni or sapio). Use the word, please. "I don't like labels" isn't the only option.
6. Bisexual characters in relationships with trans people (including non-binary people). This is really important! We bi folks get accused of being binary-minded and/or transphobic. Sometimes, that even takes the form of pitting bisexual-identified people against other multisexual people. This is an opportunity to undo the harm of that stereotype, not to mention a win for diversity.
7. Real struggles for bi-identified people. We have a rich history and culture of our own, including media. There are some real things people deal with. Balancing relationships, working out expressions of our identity, biphobia and bi erasure from both straight and gay people, gender expression, and more. These things look different depending on our other intersections, but there are some common features, just as there are in any community.
Writing bi characters can be challenging for some people. One of the difficulties is that even bi-identified people are sometimes isolated enough from our community that they don't know about what goes on. There are a number of reasons for that. If you are bi and writing bi characters, get connected. I've seen many writers rely on personal experience or stuff they've heard (please, for the love of all things writerly, stop listening to Dan Savage on bi issues---that goes for everyone, bi or not). It does help to talk to other bi folks. If you aren't bi-identified, you'll need to do a bit more digging, but that's no different from if you want to write anyone else who is part of a community or experience outside your own.