You can also use MML Editor
(along with the tools that Decoy Blimp provided), but this doesn't do everything for you, you still need some background of playing with the instruments to use and all. I had to learn the hard way.
And, I don't know if you know about MVS's Ultimate Music Tutorial
already (it's quite outdated), but this is the most that we are able to use for now until someone is able to make an updated tutorial.