Below I have listed all the things I’m currently doing to improve on my music arrangement/composition ability. I am happy to receive any feedback or advice on what you recommend and what works for you.

 
1. You must master the fundamentals of music theory.

 
2. free-midi.org. See how other songs are arranged. Download the midi and open them up on music notation software like Sibelius. Here you will clearly see what is going on with every part in a theoretical manner. This is a user submitted website, so these are not perfect, but they are still good. Also, 99% are well known hits, so you won’t find any of your obscure favourites here.

 
3. Photocopy music scores at the library. You will see the official licensed version of a song. But they usually give you the piano/voice arrangements. But it’s not bad to see different arrangements for learning sometime. You need to see how the drums, effects, harmonies and everything else come together.

 
4. Download finished music files for your software. I bought a few from http://dancemidisamples.com/ and they were quite good!

 
5. Traditional music. This is what worked only for me. Trad music is the original dance music, Celtic, klezmer, etc. See what makes people move with as little as 1-3 acoustic instruments! They didn’t have filters, oscillators, or anything like that back then. They did the job with pure organic sounds.

 
6. Listen to your favourite songs over and over and over and over again. On the first listen, concentrate on the drums. On the second, concentrate on the bass. On the third listen, concentrate on the guitars, etc.

 
7. Take one of your semi finished songs to a professional musician to see what they can add to it.