The eighth rule is "Never play to the current trend"
This is the flipside to meeting your audience halfway. On the one hand, as I mentioned before, you should never make creative decisions that will alienate your audience for the sake of your vision.
On the other hand, general audiences are not stupid, and they can tell when you are just pandering to them for the sake of a quick buck or popularity points; especially on social media. Believe me, that never works either.
Why had franchises like Disney, Star Wars, Pokémon, or Dungeons and Dragons become cornerstone of our pop culture; while their copycats often fizzle out into obscurity? The answer is that they still paired audience appeal with genuinely unique artistic vision. You still need to be true to yourself as a creator. Have and have important thing that you won't comprise on, then you can negotiate with your audience to see what your common ground is.
That said, Should you do fan art?
The problem with fan art is that, because of obvious copyright reasons, you can't depend on it as an artist; and that also means creatively.
If you draw nothing but fan art as an artist; even if you add your own spin on it, it would be like working for the big Hollywood companies without getting paid. That's not a good dynamic to have as an artist and, make no mistake, will eventually catch up to you mentally and creatively.
That all said, there are three criteria on when you should do a fan art piece.
It's only on occasion
It's part of a Fandom you genuinely love
The idea behind the fan art piece in question adds to the original, not detracts from it
As an example, let's revisit my fanart piece "Friday Night at Pizza Planet". I created this poster mainly because I wanted to see these characters in a happy, lighthearted, uneventful situation on a typical Friday night. I went into it not wanting to make it a regular thing, and despite not making any money off of it, it does greatly inform me on how I can possibly make future books in a Look-and-find format.
I would also advise against creating "Fan Characters" for a given piece. While fan Characters may be great concepts, even ones that can add to the original, the problem is that you shouldn't give your best ideas away freely to an established property. It would be like donating your vintage sports car to a demolition derby.
Instead, whatever fan Characters you created yourself...you should keep for yourself as your own original character.
The Donoverse trend is more fun