I've been playing the trombone for about a year and a half now at school, I play first in both band class and the jazz band. For my range, I can play from the low E to the double B flat or the C above it. Does anybody have any tips to help me improve?

John had a great exercice for range building, maybe ask him in PM.

A few questions. You say you are hittin Bb's or C's. You just hitting them or you could actually use them in a practical context (in a piece, scale, etude, wathever)?
Also, are you playing on a straight bone or do you have an F-attachment?

One thing is sure, if you developp a better lower register, it will also help the high register. The more relaxed your lips can be while playing, the easier and cleaner your high register will be.
So I for sure would practice what I would call the F register(F to B below bass clef) if you do have an F key, and in any case, the pedal tones (Bb 2 ledger lines below to E - or B with the attachment).
When you're pedals will be very stable, in tune and controlled, you will feel the difference in the rest of the register.

I'd suggest more long tones. Incorporate them in your every day practice, in every register with variable dynamics. I tend to keep my long tones in the ppp to mp range to develop good control (on french horn). As well as expanding range, it will help your tone and tuning (if you use a tuner while doing long tones through scales).

Hi, I'm a student in the 7th grade at Vela Middle School in Brownsville, Texas, and I have an upcoming solo named Morceau Symphonique by Andrew Guillmant. I can tell you right now, that solo is really hard. The highest note is a high C sharp(above four lines over the staff) and I am able to play it thanks to committing myself to some long tones(positions 1-7), lip slurs(positions 1-7), flow studies, and repeat it all except with legato tonguing, and stacato, and marcato, etc. Play my scales, ESPECIALLY chromatic(Low F up to High F). Repeat this on a daily basis, and I hope I helped. -Marco Villarreal