I recently acquired a valve trombone (some may have seen my post about whether or not it was worth it) and now I want to learn how to play it. I got it mostly just to mess around and have fun, but also to learn fingerings for piston valves. So my question is, where do I start? Should I just take trombone music and get used to playing it with valves instead? Or should I take some sort of trumpet method book to both learn treble clef and playing in Bb? Or is there perhaps some method book specifically for valve trombone? Any help is appreciated.

I learned valves by doubling on euphonium in high school. Grab a fingering chart and play the trombone music you already have is my suggestion. That should get you going.

Valve fingerings are the same as for baritone/euphonium, and any method book for bass clef will suffice.

The need for learning treble clef/Bb depends on what groups you plan on playing with....