For composition, I'd think it would benefit you to listen to many different works by composers. Listen and follow the score. See how they use harmony and their use of orchestration.
Don't be afraid to experiment with harmony. Use what sounds good to the ear rather than trying to stick to theoretical conventions. Play a bunch of notes on the piano, if you like the sound make a note of it. If you don't like it change part of the chord, or play a succession of chords and find the one that fits the best.
Remember that harmony also works horizontally, good harmonies are not isolated chords, but often occur as a progression of chords. You need to put the harmony in context.
Example:
Take this collection of chords:
C, D7, G, Bb, C7, F
Now put in some inversions:
C, D7/C, G/B, Bb, C7/Bb, F/A
Beethoven must have liked that

so did Rodgers and Hammerstein.