all semi-demands and bad blood aside...let me promote myself
If you don't know what to arrange, look through the
requests board and get inspired!! All the songs there are ones that people want, so you know you'll have at least one fan of your finished arrangement. If you find the song too difficult or lose interest, no one is making you finish it, so you don't have to stress about perfecting or even completing an arrangement (but maybe just don't post in the thread that you've started it unless you're sure you're going to finish it, don't wanna get anyone's hopes up). I have a whole folder of unfinished arrangements lol no one knows so no one cares! Plus, the
best part of fulfilling a request is I get to fancily format it and move it out of our very long list of wants, so actually you'll have a guaranteed TWO people thanking you!!
I'm ass at arranging so I totally get where your frustrations are coming from. As awful as I am now tho, I'm still a LOT better than when I originally started. But I only learned more by actually physically arranging; asking for help and having more experienced arrangers explain a theory or something so I could recognize it by myself next time. Levi's
recommendation of 3 track songs is a really good one, since the less voices present the easier it'll be to single out and recognize them.
You don't have to be familiar with the piece or franchise, and imo don't even have to like the song you're arranging. If your goal is improving your basic skills, you'll be motivated to arrange the most boring-ass pieces if you actively recognize the changes and progress you're making. Then, when you're a little more comfortable, you can tackle pieces you find more fun!
Looking back at my first attempts at arranging, I had a lot of questions and a lot of subsequent threads for them lol. Some quick basics imo that I found were
recognizing chords and their notes and my favorite,
notating correct rhythm groupings (which was
nonsense to me at first but once explained well made SO much sense and was very gratifying)