I've been playing the piano for about 13 years, I play many different styles from classical to jazz to film music (never really attempted contemporary classical music unless that includes electronic music). In my repertoir I have Chopin, Rachmaninoff, Debussy, Gershwin, Liszt, Beethoven, Bach, Eroll Garner, Louis Armstrong, bossa nova/the girl from ipanema, Erik Satie, Paul McCartney, The Stranglers... And I've tried to compose a piece for piano but with zero success. When I get something good by pressing random keys (literally this is one of my best methods) I then simplify the chords and strip away all the complexity to end up with only major and minor chords (and sometimes major/minor 7). I have trouble choosing what to keep and what to throw away so there is never much structure.
How do I make my composition not look like a written down improvisation and how do I achieve something that is more complexe then just min/maj chords with a melody?