When I feel cocky, I'll take a familiar old "standard" song, look at a good chord chart (
http://www.doctoruke.com/songs.html charts are always excellent) and try to link the chords together with melody notes in a way that evokes the original melody.
It's as advanced as you make it, and the more I tinker with a song, the more arrangement ideas come up - not that I can play them all, my point is that it's an open ended process..and it is working towards being a musician, not just a player.
here's a rudimentary example:
https://youtu.be/nd1iFeteyQg
hope that helps!