Rossini - William Tell Overture
General Advice
This is one of the most difficult excerpts for trombone. It requires tons of practice and listening to recordings. I also recommend recording yourself and listening back to find areas for improvement. Start this one slowly and try out different slide combinations to see which is most comfortable. I like starting in 7th position for the runs that start with a B natural.
Resources
Excerpt Recording in Orchestra - Ben Van Dijk