As you begin to read more and more music, it becomes obvious that the music is getting progressively harder. Difficult rhythms and large leaps between notes are obstacles that stand between you and a perfect performance of a piece. As far as the rhythms go, one of the best things that I have been taught was when my middle school band director made the whole band read through a page that had different rhythms all over it, one after the other. At the time I hated doing it, but I now realize that that helped me out immensely, because I knew how to play these rhythms in music when I came upon them in the fututre. There are books out that are dedicated to teaching you all kinds of rhythms and if you can get through one of those books, you'd be in pretty good shape. If you come upon a rhythm that you have not encountered, it is best to put your horn down and say the rhythm out loud, slowly at first, then, at the speed of the music. To do this, write in or simply think out loud the counting structure (many bands and orchestras use different systems-use the one recommended by your director). With a metronome beside you, sing the rhythm at half tempo, and gradually speed it up. When you have reached the tempo desired, pick up your horn and repeat the process, starting slowly and speeding up.