What makes a song beautiful is that it completely conveys YOU. What's on your mind. What's bothering you. What you just plain feel. Nothing specific is okay, but it's still what you feel, even if it's just hat you're bored. Make it you. Putting it to music is easy. Find a key first. Primarily, the feel. If it's a soft song... then you want Ab. If it's a mellow song, then go for an Eb. You want a vibrant song, use G. If you just want a twang, go for F#. Each key has it's own feel. Then fool with the progressions. If you only use three chords, great. Just throw in some extra ones to smooth the transitions. Invert too. It helps.