- How are they articulating the start of each note?
- How are they releasing each note?
- Does the volume stay the same or does it change for each note?
- What is the timbre of the note?
- Are they able to quickly and drastically get much louder or softer?
- Are they using the full range of possible articulations?
- Are they varying horizontal and vertical playing?
- Are they playing dense and sparse at different times?
- Are they aware enough of creating interesting direction in their lines?
- Do they know how to bring a rhythm section to a low simmer from a high burn?
- Are they able to consciously lay back and play on top of the beat?
- How is vibrato used and is it varied without being corny?
So often Jazz devolves into a string of connected 8th note lines, with little change in the texture that is being created. If you are always aware of the questions above while improvising then you will create interesting textural sound-scapes. Think like a sculptor or a painter instead of a musician once in a while.
How important are individual notes when the larger sound sculpture is bland and lame. Hip Be-Bop lines aren't enough to keep things interesting. Go ahead a make subtle shadings to individual notes! (Alternate fingerings and overtones are great for shading pitch and timbre)
You want to make your solos have a texture at least as complex and interesting as someone speaking a romance language.
Don't just focus on one element of texture, like dynamics. Practice being aware of all the different elements that vary texture, shift your focus consciously to one after another. Eventually it will become second nature to create interesting textures.
Ponder on This.