If you don't want to take classes (or do not have the time for them) then you'll have to experiment... which does not mean the outcome will be the one you desire. I believe that studying music formally helps a lot (it gives you the bricks with which to build the tower), and that the younger these studies start the better. Another important part is talent and predisposition. Some people are naturally gifted. Maybe you are, so give it a try. I have studied music formally since I was a child (flute, piano), but I lack talent for songwriting, so my "bricks" can only be used to badly reproduce what others have built. Sorry for the easy metaphor and good luck.