Had a jazz clinic involving the great trumpet player Marcus Printup, of the Lincoln Center Jazz Orchestra.
Here are a few things he mentioned, which should surprise none of us:
Warmup: Don't be blasting through warmup routines. Warm up is your time to get your tone beautiful, get the air moving and everything relaxed.
Playing: Play as you would sing the music, with all the nuances involved with that. Give your trumpet a VOICE, not just a sound.
Upper Range: Many aspiring lead players he's worked with neglect to do quiet long tones in the upper range. Do them -- they pay off.
Improvisation: The best thing you can do for yourself to really take off once you've begun improvisation, or at least what helped him the most was to outline the chords on the trumpet in time to the song.
Section Playing: Follow the lead player's style, listen CLOSELY and mimic his/her style as closely as you can.
Playing with a Rhythm section: Listen to the time and dynamics provided by the drummer -- he/she's guiding you. However, everyone's responsible for keeping their own internal time as well. Flow with the group.