If you’re writing a piece for piano, it is common to include a somewhat virtous solo passage. For example, use the main theme and expand on that. Such soli are also possible for any other instrument capable of playing more than one note at a time: harp, guitar, strings (to some extend).
- Convergence and Divergence
If the high notes go higher and the low notes go lower (bandwidth increases), it is called divergence. In this case make sure to fill the arising spaces between bass and melody with more texture. Convergence is the opposite situation: the high notes go lower and the low notes go higher (bandwidth decreases). In this case texture has to be eliminated between bass and melody as the distance between them shrinks. Use divergence and convergence when appropriate.
- Short dissonance
The shorter the duration of a note, the more dissonant it can be without producing an insatisfactory sound. Such short dissonances can make a piece much more vivid. Do not hesitate to use them.
- Performance techniques
Many instruments offer performance techniques like staccato, legato and pizzicato. Again, using those will make a piece more vivid. A slow, romantic string passage should be played legato, while in fast passages it is a good idea to use staccato notes.
Panning the instruments in your mix will make the sound more three dimensional. One idea is to pan the instruments according to where they are located in an orchestra from the perspective of a listener:
far left → first violins, piano
left → second violins, french horns
somewhat left → flutes, timpani
slightly left → clarinets
center → trumpets, trombones
slightly right → basoons
somewhat right → oboes
right → violas, tuba
far right → cellos, doublebasses