The great thing about music is, it's a flexible art. There are many, many different ways you can put together a piece of music, without the overall concept or quality of the music suffering.
One common thread between all methods, though, (at least in my eyes), is, be patient. Once you've set up your piece of music the way you think you want it, listen to it several times, and continue to do so for several days. (I think this is a vital step, since if your music doesn't hold up on repeat listens, what's the point of writing? Music that is excellent is endlessly listenable, and never really "gets old".)
9 times out of 10 you'll think of something you can do to improve the overall experience. Maybe this section here is a little too repetitious upon repeat listens? Or maybe this section isn't repeated enough? Oh, gosh, this section really is too short. Egad, this one is really too long! Huh, this phrase here -- what is the point of it? Does it serve to provide any sort of structure to the piece as a whole? If not, what can I do about it? Etc. Revision, revision, revision. And continue to revise it, until it reaches the point where to add something seems contrived to you, while taking away something seems to make it "miss something" to you.
When you get to the point where you've done everything you can do -- what a wonderful feeling that is :happy: You don't have any regrets about the piece, and you can hold your chin up and say, "I have written this [name of piece]. It is now set in stone -- I will move on to my next work of art."
I hope this advice and the advice of my colleagues will be beneficial to you in some way. I wish you the best of luck! :nod: