I'm pan&NB so only partially concerned.
There are a lot of tropes in BL that I'd like to not see anymore; however they often also exist in het romance so I won't discuss that.
The main BL specific thing I think it's better to avoid as an author who's not gay is building something that looks like stereotypical het romance with strong gender roles, but exchange the girl for a guy. In real life, everything exists, you will find gay couples who function like a stereotypical straight couple, but it's not the rule at all; and it's way overrepresented in BL already. Plus I think it really needs a good insight to write accurately/tastefully. I do think everyone can write about everything, but some things should probably wait for a time when the author has more maturity in the genre, especially if they are not directly concerned by what they write about.
Also, I personally think it is better not to write for a BL couple something you would not write for a het couple, i.e. something that would be uncomfortable to write if it's a girl and a guy, but that would be easier to write if it is two guys because it is less relatable/ there is a little be more distance. If it is mild, it's okay, and it can be a good way to dare more things as an author, but if it is too apparent... it can be a bit iffy. For example, it can be unnerving to read things where it is clear the author is taking their frustration out on the characters BECAUSE they are both guys.
Just my personal impressions. Not a guide how to write BL 