I started roleplaying in MMO games so the rules and so on were a bit more lax. Didn't have Discord back then, so we either only talked in-game or we had a dedicated RP forum. Now that I am doing it on the Guild my preferences have changed.

First, I look at how a person puts out the Interest Check. I don't need fancy headers or stark images or anything big, but it does tell me that when some effort is put in, they will put effort into the RP. Not saying that those who don't aren't engaged or excited.

Second, I prefer realistic-looking images for characters. Either in real life or art, but I struggle playing a game like something superhero-related and seeing someone post an anime-style image. I understand why some people don't enjoy that, but with the rise of AI technology, I am now hesitant to use art. Unless you commissioned the art yourself, you are likely still stealing from someone (unless you give credit, and even then, that's a tricky thing). If that's fine with the GM, then great, but I will likely not go into that RP.

Third, I think having deadlines helps, but I am fine with it being more lax than strict. And obviously, the understanding that real-life comes first, every time. But I have been in some RPs where there's no deadline, and the game drags on with no one doing anything and nothing getting done.

Fourth, I think 1-2 characters is more than enough for me. Even for an RP I am super excited for. Any more and I struggle with getting posts out promptly. 

Fifth, I only GMd one RP and it was a learning experience. You definitely have to balance being a fun person who listens to their players while also ensuring things move along and the story is engaging and entertaining, and it can be incredibly frustrating (I will likely never GM again).

And bonus: I prefer using color codes for dialogue for characters. It helps me keep track of things, at least, than just staring at a screen of white text