Making music is about much more than hitting the right note. Actually, hitting the right note is the least of it. After years of teaching and conducting musicians on all levels, this is the formula I have come up with in order to make music happen as soon as possible. This is of course not only a trombone lesson, but is true for all instruments.
When you play a piece of sheet music for the first time (or first few times), you probably won’t be able to get everything right. This is human and you won’t get shot for playing wrong notes. You might get shot for playing bad music though, so this is my approach to ensemble playing in general and sight-reading new music. Focus on: