Wagner - Ride of the Valkyries
Advice
This is one of those staple orchestral excerpts for trombone- one of the most famous of all time. Aside from the obvious "must-haves" like tone quality, intonation, etc., this one is really all about the rhythm. Listen to all recordings on repeat until you get the correct idea in your head. The video with Mr. Alessi has a great explanation of common rhythmic issues that players encounter and how to avoid them. Notes should be full value and longer than you think to fit the orchestral style. I recommend recording yourself and listening back to find areas for improvement.
Resources
Full Orchestra Recording - The Wicked North
Masterclass Breakdown with Thomas Leyendecker - Carnegie Hall