Composing magic and music are often the same level skill. Have the solid foundations in music, you are bound to be able to right a song in no time. 10 a day even. Have the solid foundations in magic, you should be able to create card tricks left and right. What make those songs special are that they're written in the same 4 chords. a lot of the time it's the lyrics behind it, or the personality behind it. A magic trick, like the 4 chords to music, is often just a double lift or top change, a false shuffle or count, a pass, simple gimmick of some sort. I could be wrong.. But to close, it's about your familiarity with the art. The more familiar you are with it, and the more time you've invested into the study of the art and it's creations of other artists, the easier it is for you to create works of your own. simple as that.