Switching Between Different Instruments
one of the hardest things for a brass player to do is to switch between two different brass instruments. it is no problem to switch to a woodwind, or to something like piano, because the muscles involved in playing these instruments are totally different from those used with brass horns. but to alternate between brasses, especially on a regular basis, is difficult, if not detrimental, if not done correctly. this page contains my musings on how the least damage can be done when switching.
i myself play trombone and tuba daily. this can be very tricky, especially in a concert setting, when i am required to play both horns one right after the other. the best way for me to handle this is to buzz in between instruments. this keeps my mouth warm, but also allows it to adjust to a different sized mouthpiece gradually.
a trombone switching to euph and vice versa does not need to worry much about the change, as the mouthpieces are the same. however, a horn player who also plays tuba is going to need some serious, slow warming up in between to avoid damage to the embouchure.
if you are playing two different instruments with regularity, consider easing up on your secondary horn. for instance, when i had a tuba audition coming up, for about a week i would only play my trombone very reservedly, not taking solos and playing only around mezzo piano.