Meditation by Vladimir Bakaleinikoff

Classic Festival Solos Volume 2 for Trombone (Euphonium)
Don't let the 12/8 time signature scare you - Give the dotted quarter note the beat (as you hear it in the piano part) and subdivide to the eighth note pulse 1-two-three-4-five-six-7...
Towards the end when it has the low F, I would recommend playing F's in 6th position for a little bit to help with resonance, tuning and slide technique.