Looking through the wrong end of the telescope?
Much like a comment above suggests, I don't really get this. Most conventional music has rules - those rules are fairly easy to quantify: start with any note, use that as your base key. Pick major or minor (or melodic, enharmonic, whatever) to give you a scale for that key (the notes to use are rule-based too). Pick 1st, 3rd and 5th of your current scale to give you a simple chord that works with it; add a 7th or occasional minor 3rds if you want to be bluesey, etc. Now and again, change your scale root to the 4th note, then the 5th of your base key - bingo, you've got a 12-bar-style progression - the basis of much rock and/or roll music. Noodle around with the notes in your key and generate some sort of melody. Add in some alternate progressions for variety or as a middle eight (again, there are established patterns for all of this). Does it sound OK? If not, start again and try other combinations. This is pretty much entirely how I learned to improvise Jazz/Blues piano