Currently, I'm working through "40 Progressive Etudes for Trombone" by Sigmund Hering plus some scales and a medley of Christmas music.
I'm looking forward to starting to take a look at Arban's famous method for slide and valve trombone and baritone (bass clef) soon, which I found based on the recommendation of a longterm family friend and trombone player. He also pointed out that he enjoys playing the Bach cello concertos, transcribed to trombone. I'm taking inspiration from this performance of them: SUITE Nº1 IN G MAJOR (BWV 1007) J. S. BACH FOR TROMBONE ALONE BY JAVIER YERA (though I'm so far off from this level at the moment). I think this portion of it will be a good place for me to start: Cello Suite No.1 in G major BWV1007:I Präludium For Trombone.
I'm looking forward to making progress, to learning from the larger trombone community. Another thing I'm looking at is Douglas Yeo's FAQ.
If you have any favorite resources for improving your trombine skills, I'd love to hear about them. Thank you.