In case anyone is interested, here is the method I use when making arrangements of music (such as video game or anime songs).
1. I think of what general genre the piece will be in. The broadest choice I have is between piano or digital. I won't go into piano arrangements for now, since I don't feel qualified. For digital, I do not choose a specific style- often times, the style of what I just did is only apparent after I'm finished with the work. Thus, I decide beforehand if I want orchestral, trance, dnb, or jazz, for instance, but not any specific subgenre
2. I set up a solid introduction. The introduction, for me, either involves bringing the different instruments of the song in groups every few measures, or having them start out at the same time, but use an improvised melody. Sometimes, I will combine the two; for instance, in a recent Phantasy Star 4 remix, I started out with some dissonant synths playing an improvised melody on the song's chord progression, as the other instruments (bass, drumline, lead) came in one by one.
3. I implement the main melody. I don't like doing too much variation on the melody. My focus here is on creating an interesting, enjoyable background for it, while making sure that it is emphasized enough. This is probably where I spend the most time, as selecting the perfect instrument, sample, or synth for the job is tough. I also try to vary the background and harmony a bit, to ensure that things don't get boring.
4. If the melody is long, I try to chop it up, interspersing it with solos or improv sections. If not, I do a lot of filling it with various synths and other instruments, while having repetition of the melody (with variation) in various parts.
5. I don't spend that much time on the ending. I usually have some sort of buildup, then a final chord or drum hit, or something. If not, I fade out in the same way that I fade the song in.
so.. that's basically how I do it. maybe this will help someone (probably not

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